NCERT Solutions for Class 10 Science Chapter 9 - Model Test Paper 3

Share with your friends Share Share Share twitter

Answer:

Iron objects when they are in contact with air and moisture they are prone to rust. Thus, to prevent the rusting of iron, iron objects are painted as the upper layer gets protected from air and moisture.

Answer:

(a) The concave mirrors are used in the headlights of a car to get powerful beams of light. 

(b) Convex mirrors are used as rear view mirror of a car because convex mirrors always form an erect and diminished image. Which helps the driver to see a wider view.

Answer:

Valence shell of element X contains three electrons.

(a) The formula of chloride of element X will be XCl₃.

(b) The formula of an oxide of element X will be X₂O₃.

Answer:

Focal length of concave lens = 20 cm

Object distance = 50 cm

Using lens formula, $\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

$$\begin{gathered} \Rightarrow \frac{1}{v}=\frac{1}{-20}+\frac{1}{-50}=-\frac{7}{100} \\ \Rightarrow v=-\frac{100}{7} \mathrm{cm} \end{gathered}$$

The image formed is virtual, erect and diminished in size.

Answer:

Advantages of constructing large dams -

• The water stored in dams is used for irrigation throughout the year, irrespective of the season. For example, the Indira Gandhi Canal originates in Bhakra dam and provides water to several areas in Rajasthan.
• Dams are also equipped with turbines and generators to produce hydroelectricity.

Answer:

(a) Element A is metal, as it belongs to the alkali metal group(1) of the modern periodic table.

(b) Element D is a non-metal, as it belongs to the carbon family(14) of the modern periodic table.

(c) An ionic bond is formed by permanent transfer of electrons, so element "A" will lose one electron to achieve noble gas configuration and element "B" will gain an electron to achieve the noble gas configuration. So, ionic bond forms between A and B.

(d) The covalent bond is formed by sharing of electrons, so element "B" requires an electron to achieve the noble gas configuration and "D" requires four electrons to achieve the noble gas configuration. Hence,  D will form four single bonds with four molecules of B.

(e) Element "B" will form an anion of valency 1, as it will accept one electron from other donating species.

(f) Element "C" is a noble gas element, as its outer most shell is fully filled.
 

Answer:

When dilute hydrochloric acid reacts with zinc metal, zinc will displace hydrogen from hydrochloric acid and form zinc chloride. It is accompanied by the release of hydrogen gas.

$2\mathrm{Zn}\left(\mathrm{s}\right)+2\mathrm{HCl}\left(\mathrm{aq}\right)\to {\mathrm{ZnCl}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$ 

When we place a burning candle near the mouth of the test tube a pop-up sound is produced which confirms the presence of hydrogen gas in solution.
Sodium metal on reaction with cold water gives sodium hydroxide and hydrogen gas will evolve.

$2\mathrm{Na}+2{\mathrm{H}}_2\mathrm{O}\to 2\mathrm{NaOH}+{\mathrm{H}}_2$

Answer:

(a) As we move from left to right in a periodic table size of element decreases due to the increase in the number of electrons in the shell, they are pulled strongly towards the nucleus. Hence, the bigger atom is "a".

(b) Valency can be defined as the number of electrons available for bond formation.
Valency of k = 3
Valency of o = 1
Hence, "k" have higher valency. 

(c) On movind left to right in a periodic table metallic character decreases.
On moving down the group metallic character increases.
So, "i" will be more metallic.

(d) On moving left to right in a periodic table non-metallic character increases.
On moving down the group non-metallic character decreases
So, "g" will be more metallic.

(e) Valency can be defined as the number of electrons available for bond formation.
Valency of f and n is 2.

(f) "h" and "p" represents noble gas.

Answer:

We seperately dip red litmus paper in three solutions, the basic solution will turn red litmus to blue. After that we use that blue litmus in other two solutions to test acidic solution, when we dip blue litmus in two solutions acidic solution will turn blue litmus to red and the remaining solution will be distilled water.

Answer:

(a) When the object is placed at the radius of curvature of a concave mirror, then the image formed is equal in size with the object. 

(b) Concave mirrors are used in motor vehicle headlights to reflect strong beams of light.

(c) Radius of curvature of the lens = 20 cm

Focal length = 10 cm

Object distance = 15 cm

Using mirror formula, $\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$

$$\begin{gathered} \Rightarrow \frac{1}{v}=\frac{1}{-10}-\frac{1}{-15}=-\frac{1}{30} \\ \Rightarrow v = 30 \mathrm{cm} \end{gathered}$$

Magnification of the mirror is given by the relation,

 $$\begin{gathered} m = -\frac{v}{u}=-\frac{30}{15}=-2 \\ \Rightarrow m=-2=\frac{h_{\mathrm{i}}}{h_{\mathrm{o}}} \\ \Rightarrow h_{\mathrm{i}}=-2h_{\mathrm{o}}=-2\times 1 \mathrm{cm} = -2 \mathrm{cm} \\ \Rightarrow {\mathrm{h}}_{\mathrm{i}}=-2 \mathrm{cm} \end{gathered}$$

Nature of the image is virtual, inverted and enlarged.

Answer:

(a) Fleming's right-hand rule is illustrated in the figure. 

(b) (i) The motion of the conductor.
(ii) Magnetic field
(iii) Current

Answer:

(a)

 

(b) The image formed is real.

(c) The image formed is enlarged.

Answer:

Human digestive system



(a) Water is absorbed in the large intestine.
(b) Food is absorbed in the small intestine.

Answer:

Hydrochloric acid is produced in the stomach. Production of too much of acid in the stomach leads to the irritation of the stomach lining. This in turn can lead to formation of ulcers in the stomach. Excess acid can be neutralised by taking antacids which are basic in nature.

Answer:

Fats and oils when kept for a long time get oxidized because of which the taste and odour of food containing these fats changes and it becomes unfit for consumption. This is called rancidity.
Following ways can prevent rancidity:
i) Storing food in an airtight container.
ii) Antioxidants are added to foods containing fats and oils.
iii) Flushing packed food items with an inert gas like nitrogen.

When fatty substances are exposed to air, its unsaturated components are converted into hydroperoxides, which break down into volatile aldehydes, esters, alcohols, ketones, and hydrocarbons, some of which have disagreeable odours. 


 

Answer:

(a) 
(i) When sodium is burnt in chlorine, due to addition reaction sodium chloride is formed.
$2\mathrm{Na}+{\mathrm{Cl}}_2\to 2\mathrm{NaCl}$
(ii) When this sodium chloride is electrolyzed, sodium chloride is decomposed into its ionic state as sodium ions and chloride ions.
$$\begin{gathered} \mathrm{At} \mathrm{cathode}: \mathrm{Na}\to {\mathrm{Na}}^{+}+{\mathrm{e}}^{-} \\ \mathrm{At} \mathrm{anode}:\mathrm{Cl}+{\mathrm{e}}^{-}\to {\mathrm{Cl}}^{-} \\ \mathrm{Net} \mathrm{reaction}: \mathrm{Na}+\mathrm{Cl}\to \mathrm{NaCl} \end{gathered}$$ 
So, it is a decomposition reaction.

(b) When hydrogen gas is passed over heated copper oxide, then the black copper oxide is reduced and red-brown copper metal is obtained. The reaction involved can be shown as:
$\mathrm{CuO}+{\mathrm{H}}_2\to \mathrm{Cu}+{\mathrm{H}}_2\mathrm{O}$
As copper is losing oxygen and hydrogen is accepting oxygen, so copper is reduced and hydrogen is oxidized.

(c) When zinc is added to a solution of iron sulphate, then it would displace iron from the solution and form zinc sulphate.
$\mathrm{Zn}+{\mathrm{FeSO}}_4\to {\mathrm{ZnSO}}_4+\mathrm{Fe}$
This reaction is an example of a displacement reaction because zinc is more reactive than iron, zinc will displace iron from the solution.

 

Answer:

(a) The functional group present in an aldehyde will be carbonyl group and in carboxylic acid will be carboxyl group.

(b) Ethanol and ethanoic acid can be distinguished by reaction with sodium hydroxide. Ethanol does not react with sodium hydroxide, but ethanoic acid reacts with sodium hydroxide to form sodium ethanoate and water.
${\mathrm{CH}}_3\mathrm{COOH}+\mathrm{NaOH}\to {\mathrm{CH}}_3\mathrm{COONa}+{\mathrm{H}}_2\mathrm{O}$
Ethanol has a sweet and pleasant smell but ethanoic acid has a pungent odour.

(c) When ethanoic acid is warmed with ethanol in the presence of a few drops of concentrated sulphuric acid, we will get a sweet smelling ester ethyl ethanoate.
${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}+{\mathrm{CH}}_3\mathrm{COOH}\stackrel{{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }{\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5+{\mathrm{H}}_2\mathrm{O}$

(d) When a piece of sodium metal is added to ethanol, sodium ethoxide is formed with the evolution of hydrogen gas.
$2{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}+2\mathrm{Na}\to 2{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{ONa}+{\mathrm{H}}_2$

(e) By acidic hydrolysis of ethanol, dehydration of ethanol will occur which lead to the formation of ethene.
${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}\stackrel{{\mathrm{H}}^{+}/{\mathrm{H}}_2\mathrm{O}}{\to }{\mathrm{CH}}_2={\mathrm{CH}}_2$

 

Answer:

(a) In a series combination, resistances are connected by an end to end such that the current flowing through all of them is equal. Whereas in a parallel combination, the resistances are connected in such a manner that they get an equal voltage.

(b) In a parallel combination, the reciprocal of net resistance is equal to the sum of reciprocals of individual resistances. Hence, in a parallel combination of resistances, the net resistance is smaller than any of the individual resistances. 

(c)  Two resistances of 2 Ω each should be connected in parallel. The net resistance of the parallel combination of both the resistors would be equal to 1 Ω. 

$$\begin{gathered} \frac{1}{R_{\mathrm{net}}}=\frac{1}{R_1}+\frac{1}{R_2}=\frac{1}{2}+\frac{{\displaystyle 1}}{{\displaystyle 2}}=1 \\ \Rightarrow R_{\mathrm{net}}= 1 \mathrm{\Omega } \end{gathered}$$

(d)

(i) As we can see in the figure, Resistances R₂ and R₃ are connected in parallel.

The net resistance of the parallel combination = $\frac{R_2{R}_3}{R_2+R_3}=\frac{8\times 12}{8+12}=\frac{96}{20}=4.8 \mathrm{\Omega }$

Now, the equivalent resistance of the whole circuit is the series combination of R₁ and net resistance of parallel combination.

Equivalent resistance = $7.2 \mathrm{\Omega } +4.8 \mathrm{\Omega } =12 \mathrm{\Omega }$

(ii) Current in the circuit = $\frac{\mathrm{Total} \mathrm{voltage} \mathrm{applied}}{\mathrm{Total} \mathrm{resistance}}=\frac{6 \mathrm{V}}{12 \mathrm{\Omega }}=0.5 \mathrm{A}$

(iii) The potential difference across R₁ = Current through R₁ $\times$ Resistance of R₁ = $0.5 \mathrm{A} \times 7.2 \mathrm{\Omega }=3.6 \mathrm{V}$

Answer:

(a) When an electric current flows in a circuit, it produces heat across the resistive elements of the circuit. This is called the heating effect of current. The heat produced depends on the following factors:

(i) Current flowing the circuit.
(ii) The resistance of the circuit.

(b) The heating element of the heater is made up of an alloy which has very high resistance. So, when current flows through the heating element, it becomes too hot and glows red due to the heating effect of current. But, the resistance of cord which is usually of copper or aluminium is very low, so it does not glow.

(c) The heat produced in the geyser = $I^{2}Rt$ (Where 'I'  is current, 'R' is the resistance and 't' is the time for which the current flows)

In the given case, Resistance of the geyser = 20 Ω

Current flow = 5 A

Time of current flow = 2 minutes = 120 seconds

Heat produced = $(5{)}^2\times 20\times 120=60 \mathrm{KJ}$

(d) Commercial unit of electric energy is 'kWh'. $1 \mathrm{kWh} = 3.6\times {10}^6 \mathrm{J}$
 

Answer:

The circulatory system consists of the following organs - four-chambered heart, a network of branching blood vessels and blood.
The blood vessels are of three types - veins, arteries and capillaries.


 

Double circulation is the process of passing blood twice through the heart in one cycle. It occurs in bigger organisms like mammals and birds requiring more metabolic energy.

The four-chambered heart in humans contains two auricles (left and right) and two ventricles (left and right). The left part of the heart contains oxygenated blood and the right part of the heart contains deoxygenated blood. Thus, blood passes two times in one complete circuit—one with oxygenated blood and the other with deoxygenated blood. This is double circulation. The double circulation system prevents the mixing of oxygenated and deoxygenated blood.

Answer:

(a) Puberty is the process in which the body attains sexual maturity by having well-developed sex organs, and becomes capable of reproduction.

Changes that occur in females during puberty:

(i) development of breasts

(ii) softening of voice

(iii) ovum begins to mature with the onset of puberty.

(iv) occurrence of the menstruation cycle (first menstrual flow beginning at puberty is called menarche, and the stoppage of menstruation at the age of 45 − 50 years is called menopause.)
 

Changes that occur in males during puberty:

• Under the influence of hormones, the larynx develops prominently. The vocal cord become longer and thicker in boys, causing the voice to become hoarse.
• Growth of hair in other areas of skin like underarms, face, hands, and legs.
• Enlargement of the testicles followed by penis.
• Testes grow and start producing sperms.

Testes - They are located outside the abdominal cavity within a pouch called the scrotum. The function of the testes is to produce sperms and a hormone called testosterone, which brings about secondary sex characteristics in boys.

Vas deferens - It carries the sperms from the testes to the urethra. It also receives the ducts, which bring products from the seminal vesicles and prostate glands.

Seminal vesicles and prostate glands - The fluids from these organs provide nutrients in the form of fructose, calcium, and some enzymes. The sperms produced in the testes are carried by the vas deferens. The secretions from the seminal vesicles and prostate glands lubricate the sperms.

Testes are located outside the abdominal cavity, within a pouch called the scrotum. For the production of sperms, testes require a temperature that is 2–2.5 °C lower than the temperature of the rest of the body. That is why testes are protected inside the scrotum. 

Role of seminal vesicles and prostate gland -

(i) Seminal vesicles - The secretions of seminal vesicles contain many proteins and enzymes and thus provide nutrition to the developing sperms.

(ii) Prostate gland - The prostate gland secretes a slightly alkaline fluid that lubricates the sperms and neutralises the acidity of the vaginal tract.

Answer:

5 divisions of voltmeter scale = 1 V

1 division of voltmeter scale = 0.2 V

Hence, 12 divisions of voltmeter scale = 2.4 V
 

Answer:

(a) The touching of a naked live wire and a naked neutral wire is termed as short-circuiting.

(b)  When the naked wires touch each other directly, the resistance of the circuit becomes negligible. That's why, short-circuiting results in a high flow of current in the circuit, which sometimes damages the electrical components. 

(c) During short-circuiting, the resistance of the circuit becomes negligible. So, the current in the circuit becomes too high. 

(d) The earth wire protects the person from getting an electric shock.

Answer:

(a) Lead nitrate is of white colour.

(b) When lead nitrate is heated, it is decomposed into three simpler products - yellow coloured lead oxide, brown fumes of nitrogen dioxide and oxygen.

$\underset{\mathrm{white}}{\mathrm{Pb}({\mathrm{NO}}_3{)}_2}\left(\mathrm{s}\right)\stackrel{\mathrm{heat}}{\to }\underset{\mathrm{yellow}}{\mathrm{PbO}\left(\mathrm{s}\right)}+\underset{\mathrm{brown} \mathrm{fumes}}{{\mathrm{NO}}_2\left(\mathrm{g}\right)}+{\mathrm{O}}_2\left(\mathrm{g}\right)$

(c) Brown coloured gas is nitrogen dioxide.

(d) Yellow coloured solid formed is lead oxide.

 

Answer:

(a) When student adds liquid X in zinc granules, a gas Y is produced with a pop sound, which means that gas Y will be hydrogen. 
So, liquid X must be a hydrogen-containing compound, it can be hydrochloric acid.

$\mathrm{Zn}+2\mathrm{HCl}\to {\mathrm{ZnCl}}_2+{\mathrm{H}}_2$

(b) Gas Y will be hydrogen.

(c) Properties of hydrogen gas:
(i) It easily reacts with oxygen to form water.
(ii) It is used as an energy medium in lot of combustion reactions.
(iii) It is used as rotor coolant in electrical generators.

Answer:

(a) These people must be suffering from goitre.
(b) This disease is caused due to deficiency of thyroxine hormone.
(c) The food grown in hilly areas is deficient of iodine because lot of iodine leaches out from the soil in this region. As a result of which, people suffer from goitre in hilly regions.
(d) This disease can easily be prevented by consuming iodised salt in their daily diet.

Answer:

(a) Initially, the plant is kept in dark for 24 hours to destarch the leafs.
(b) A part of destarched leaf is covered with black paper so that the light does not reach that region and photosynthesis does not occur.
(c) The chlorophyll is removed from the leaf green leaf before testing by boiling it in alcohol.
(d) The reagent used to test the presence of starch is called iodine.