Bond dissociation energies of $HF, HCl, HBr$ follow the order:

In covalency:

$BCl_3$ does not exist as a dimer,whereas $BH_3$ exists as a dimer $(B_2H_6)$ because ....

In which of the following is $p\pi - d\pi$ bonding observed?

The octet rule is not followed in

The electronic configuration of $X$ and $Y$ are given below:
$X: 1s^2 2s^2 2p^6 3s^2 3p^3$
$Y: 1s^2 2s^2 2p^6 3s^2 3p^5$
Which of the following is the correct molecular formula and type of bond formed between $X$ and $Y$?