Concept of Atomic structure

Question:

A positron is emited from !! 23Na_11 !!. The ratio of the atomic mass and atomic number of the resulting nuclide is:

(a) !!23/10!!

(b) !!22/10!!

(c) !!23/12!!

(d) !!22/11!!

Solution

Positron emission or beta plus decay (!!beta+!! decay) is a type of radioactive decay in which a proton inside a nucleus is converted into a neutron while releasing a positron and an electron neutrino !!(V_e)!!

!! 1p_1 rarr 1n_0 + 0e_1 +V_e!!

!!0e_1 +V_e!! are released and proton inside the atom turns into a neutron.

!! 23Na_11 rarr 23Na_10 + e^+ +V_e!!

So atomic number decreases by one but atomic mass remains constant.
Atomic mass/atomic number !!= 23/10!!

Therefore, option (a) is correct.