Board Paper of Class 10 2008 Science (SET 1) - Solutions

Balance the following chemical equation:

Why is respiration considered an exothermic process?

How does the flow of acid rain water into a river make the survival of aquatic life in the river difficult?

Draw the following diagram in your answer book and show the formation of image of the object AB with the help of suitable rays.

Why is the series arrangement not used for connecting domestic electric appliances in a circuit?

Out of 60 W and 40 W lamps, which one has a higher electrical resistance when in use?

Write the chemical formula for washing soda. How may it be obtained from baking soda? Name an industrial use of washing soda other than washing clothes.

Give an example of a decomposition reaction. Describe an activity to illustrate such a reaction by heating.

Draw ray diagrams to represent the nature, position and relative size of the image formed by a convex lens for the object placed:

(a) at 2F₁.

(b) between F₁ and the optical centre O of lens.

What is meant by the term, ‘magnetic field’? Why does a compass needle show deflection when brought near a bar magnet?

(a) Why are covalent compounds generally poor conductors of electricity?

(b) Name the following compound:

(c) Name the gas evolved when ethanoic acid is added to sodium carbonate. How would you prove the presence of this gas?

(a) What are amphoteric oxides? Choose the amphoteric oxides from amongst the following oxides:

Na₂O, ZnO, Al₂O₃, CO₂, H₂O

(b) Why is it that non-metals do not displace hydrogen from dilute acids?

Two lamps, one related 60 W at 220 W at 220 V and the other 40 W at 220 V, are connected in parallel to the electric supply at 220 V.

(a) Draw a circuit diagram to show the connections.

(b) Calculate the current drawn from the electric supply.

(c) Calculate the total energy consumed by the two lamps together when they operate for one hour.

(a) Distinguish between the terms “overloading and short circuiting” as used in domestic circuits.

(b) Name the device used to protect the electric circuits from overloading and short circuit.

On the basis of Mendeleev’s Periodic Table given below, answer the questions that follow the table:

(a) Name the element which is in

(i) I^st group and 3^rd period.

(ii) VII^th group and 2^nd period.

(b) Suggest the formula for the following:

(i) oxide of nitrogen

(ii) hydride of oxygen

(c) In group VIII of the Periodic Table, why does cobalt with atomic mass 58.93 appear before nickel having atomic mass 58.71?

(d) Besides gallium, which two other elements have since been discovered for which Mendeleev had left gaps in his Periodic Table?

(e) Using atomic masses of Li, Na and K, find the average atomic mass of Li anf K and compare it wit the atomic mass of Na. State the conclusion drawn from this activity.

(OR)

(a) Why do we classify elements?

(b) What were the two criteria used by Mendeleev in creating his Periodic Table?

(c) Why did Mendeleev leave some gaps in his Periodic Table?

(d) In Mendeleev’s Periodic Table, why was there no mention of Noble gases like Helium, Neon and Argon?

(e) Would you place the two isotopes of chlorine, Cl-35 and Cl-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify you answer.

(a) What is meant by dispersion of white light? Describe the formation of rainbow in the sky with the help of a diagram.

(b) What is hypermetropia? Draw ray diagrams to show the image formation of an

object by:

(i) Hypermetropic eye.

(ii) Correction made with a suitable lens for hypermetropic eye.

OR

(a) Give reason for the following:

(i) Colour of the clear sky is blue.

(ii) The sun can be seen about two minutes before actual sunrise.

(iii) We cannot see an object clearly if it is placed very close to the eyes.

(b) What is Presbyopia? Write two causes of this defect.