Sir can u tell... Will atomic mass of elements having atomic no above 20 will be given in JEE? also IS percentage yield=percentage impurity? (important one)
Do we also have to remember the chemical reactions?

Dear Student,

Yes, atomic masses of elements having atomic number greater that 20 are given in JEE. However, it is better if you memorise some masses of some of the elements. The atomic mass of an element is nearly double of its atomic number.

No, percentage yield and percentage impurity are not the same thing. Percentage yield is the amount of product we obtain from a reaction. The product may contain even some impurities.

Percentage impurity is the amount of pure product obtained in the chemical reaction. 
$$\begin{gathered} \mathrm{Percent} \mathrm{yield} = \frac{\mathrm{actual} \mathrm{mass} \mathrm{obtained}}{\mathrm{calculated} \mathrm{mass}}\times 100 \% \\ \mathrm{Percent} \mathrm{purity}=\frac{\mathrm{mass} \mathrm{of} \mathrm{pure} \mathrm{product}}{\mathrm{mass} \mathrm{of} \mathrm{impure} \mathrm{product} \mathrm{obtained}}\times 100 \% \end{gathered}$$

Yes, you need to remember chemical reactions. Although it is not necessary to remember all of them, however try to learn some of the important chemical reactions.