Define bond angle and bond length.

Considering $\mathrm{x}$-axis as the internuclear axis, which out of the following will not form a sigma bond and why?

(a) $1\mathrm{s}$ and $1\mathrm{s}$ (b) $1\mathrm{s} \mathrm{and} 2{\mathrm{p}}_{\mathrm{x}}$ (c) $2{\mathrm{p}}_{\mathrm{y}} \mathrm{and} 2{\mathrm{p}}_{\mathrm{y}}$ (d) $1\mathrm{s} \mathrm{and} 2\mathrm{s}$.

In which of the following molecule, is the London force likely to be most important in determining $\mathrm{m}.\mathrm{p}.$ and  $\mathrm{b}.\mathrm{p}.$ and why?

$\mathrm{ICl}, {\mathrm{Br}}_2, \mathrm{HCI}, {\mathrm{H}}_2$ and $\mathrm{CO}$.