Polarizibility of noble gases increases down the group because of increase of distance of electrons from nucleus. Thus He (first member of group) is least polarized.

CCl₃NO₂

\(SO_{2}+Cl_{2}\overset{Sun\, light}{\rightarrow}SO_{2}Cl_{2}(Sulphurylchloride)\)

The order of bond energy is Cl – Cl > F –F >Br – Br > I – IT he small value of bond energy in F₂ than Cl₂(anomaly)is due to smaller size of F atom which leads to inter-electronic repulsions.

Longer bond length means weaker bond energy i.e.less bond dissociation energy or more reactivity. Larger the size of anion more will be bond length thus the order of reactivity is HI > HBr > HCl.

\(H_{2}SO_{4}+SO_{3}\rightarrow \underset{Oleum}{H_{2}S_{2} O_{7}}\)