One gram-mole of any gas contains Avogadro’s number of atoms/molecules. Hence, one gram-mole of Hydrogen gas and Helium gas weigh two grams and three grams respectively. 1g H₂ = 1/2 g-mol H₂; 1g He = 1/3 g-mol He. Thus, one gram of Helium has least number of atoms.

Bond angle is 109° for symmetric molecules like methane. However, it is known that repulsion between a lone pair and a bond pair is more than that between two bond pairs. Hence, bond angle is reduced from 109° so as to experience minimum repulsion from lone pairs.

Ionization energy is energy required by an isolated gaseous atom to lose least tightly bound electron to form a cation. It decreases down group as atomic size increases.

For principal quantum number 3, only possible values of azimuthal quantum number are 0, 1, and 2. Azimuthal quantum number of an f-orbital is 3.

The coulombic force of attraction is inversely proportional to square of a distance between charges. As internuclear distance in a bond increases, force of attraction between nuclei and electrons decreases.

Due to addition of one shell on moving down a group, neighbourhood of atom is better shielded by electrons from an attractive pull of nucleus.

Radon is a radioactive noble-gas at room temperatures. It is one of densest gases and only naturally occurring radioactive gas. However, its daughter nuclei are solids. Not many compounds of Radon are known.

Van der Waals radius is half internuclear distance between two non-bonded atoms on ir closest approach whereas covalent radius is half bond length of a homo-nuclear molecule. Since distance between two bonded atoms is less than non-bonded atoms, hence answer.

At any specified temperature, molar volume for every gas is same. However, CO₂(g) has higher molar weight than O₂(g) which results in higher density.

Polymeric molecules are aggregates of a large number of monomer units and possess high molecular mass. Hooke’s law generally does not apply to polymers as stress developed is not directly proportional to deformation. Due to low densities, strength to mass ratio of polymers is often comparable to metals and ceramics.