Atomic no. (Z) = 19 and Atomic mass (A) = 39
No. of neutrons = (A - Z) = (39 - 19) = 20
No. of electrons = Number of protons = Atomic number

The permanent change in which one compound is transformed into other compound have different properties is known as chemical change.

Two important characters are:

a. It is irreversible change.
b. New compound having different properties are formed.

Atomic no. (Z) = 13 and atomic mass (A) = 27
No. of neutrons = A-Z = 27 - 13 = 14
No. of electrons = 13 - 3 = 10

Al atom loses 3e^- to form Al⁺³.

Entrance should be fully based on the things that you learnt till Class 10 but these days as the competition is increasing some colleges has been found including the questions from class 11 as well like the basic questions which will bridge both 10 and 11. And that's why we saw several students indulging in bridge course classes and all. If you have completed the contents upto class 10 then you can see the notes of 11 class as well it will surely help somehow in entrance. For further more...