Write down the electronic configuration of the following:

(a) ₁₂²⁴X

(b) ₁₅³¹Y

Write down the number of electrons in X and neutrons in Y.

Rutherford's alpha-particle scattering experiment led to the discovery of :

1. Electron
2. Proton
3. Atomic nucleus
4. Neutron

Which of the following is the correct electronic configuration of potassium ?

1. 2, 8, 9
2. 8, 2, 9
3. 2, 8, 8, 1
4. 1, 2, 8, 8

The mass number of an atom whose unipositive ion has 10 electrons and 12 neutrons is :

1. 23
2. 22
3. 20
4. 21