1 molecule of oxygen (O₂) = 2 atoms of oxygen
1 molecule of ozone (O₃) = 3 atoms of oxygen
In flask P:
1 mole of oxygen gas = 6.022 x 10²³ molecules
0.5 mole of ozone gas = 6.022 x 10²³ x 0.5 molecules
= 6.022 x 10²³ x 0.5 x 2 atoms
= 6.022 x 10²³ atoms
In flask Q:
1 mole of ozone gas = 6.022 x 10²³ molecules
0.4 mole of ozone gas = 6.022 x 10²³ x 0.4 molecules
= 6.022 x 1023 x 0.4 x 3 atoms
= 7.23 x 10²³ atoms
∴ Flask Q has a greater number of oxygen atoms as compared to flask P.

Average atomic mass of Carbon \(=12 \times\left(\frac{98.9}{100}\right)+13 \times\left(\frac{1.1}{100}\right)\)
=12 x 0.989 + 13 x 0.011
=11.868 + 0.143
=12.011 amu.

The average atomic mass of an element in the weighted average of the masses of its naturally occurring isotopes.
Average atomic mass = (Mass of 1^st Isotope x % abundance of 1^st Isotope)+
(Mass of 2^nd Isotope x % abundance of 2^nd Isotope).

Relative atomic mass of an element is the ratio between the average mass of its isotopes to 1/12th part of the mass of a Carbon-12 atom. It is denoted as A. It is otherwise called as Standard Atomic Weight.
AR = \(\frac{Average \ mass \ of \ the \ Isotopes \ of \ the \ element}{1/12th \ of \ the \ mass \ of \ one \ carbon \ atom}\)

The sum of the number of protons and neutrons of an atom is called its mass number.