Question

what is the general ratio of protons to neutrons in stable isotopes of elements of the first two periods of the periodic table?

a) 1 : 2
b) 1 : 1
c) 2 : 3
d) 2 : 1

Explanation:

Step1: Recall stable isotopes in first two periods

For elements in the first two - periods of the periodic table, such as hydrogen - 1 ($^1H$ with 1 proton and 0 neutrons), helium - 4 ($^4He$ with 2 protons and 2 neutrons), lithium - 7 ($^7Li$ with 3 protons and 4 neutrons), beryllium - 9 ($^9Be$ with 4 protons and 5 neutrons), boron - 11 ($^{11}B$ with 5 protons and 6 neutrons), carbon - 12 ($^{12}C$ with 6 protons and 6 neutrons), nitrogen - 14 ($^{14}N$ with 7 protons and 7 neutrons), oxygen - 16 ($^{16}O$ with 8 protons and 8 neutrons), fluorine - 19 ($^{19}F$ with 9 protons and 10 neutrons), neon - 20 ($^{20}Ne$ with 10 protons and 10 neutrons). In general, for light elements (first two periods), the number of protons and neutrons in stable isotopes is approximately equal.

Answer:

B. 1 : 1