Which of the following pairs are isotopes? Give reasons for your choice:

(i) or (ii)

What is the number of valence electrons in:

(a) sodium ion, Na⁺

(b) oxide ion, O^2-

Atom A has a mass number 209 and atomic number 82.

Atom B has a mass number 209 and atomic number 83.

(i) How many protons atom A has?

(ii) How many protons atom B has?

(iii) Are atoms A and B isotopes of the same element?

Three different atoms of oxygen are represented as:

(i) What do the subscripts (lower figures) and superscripts (upper figures) represent?

(ii) What factor is responsible for the change in the superscripts 16, 17 and 18, though the element is the same?

(iii) What is the usual name for such atoms of an element?

(iv) Give the nuclear composition of

The atomic species A and B have different number of protons but the same number of nucleons. On the other hand, the atomic species X and Y have the same number of protons but different number of nucleons. Which pair is an example of isobars? Why?