What is the number of sigma bonds in $P_4O_{10}$?

The decreasing order of bond dissociation energies of $C-C$, $C-H$, and $H-H$ bonds is:

Which of the following species are isoelectronic?
$I. CH_3^+$
$II. NH_2^-$
$III. NH_4^+$
$IV. NH_3$

The number of bonds between sulphur and oxygen atoms in $S_{2}O_{8}^{2-}$ and the number of bonds between sulphur and sulphur atoms in rhombic sulphur,respectively,are

Identify the statement$(s)$ which is(are) not correct from the following:
$a)$ $NH_3$ and $H_3O^+$ are isostructural
$b)$ $ClF_3$ has $T$-shape
$c)$ $O_2$ molecule is paramagnetic
$d)$ Bond order of $N_2^+$ is more than $N_2$

Number of electron-deficient molecules among the following $PH_{3}$,$B_{2}H_{6}$,$CCl_{4}$,$NH_{3}$,$LiH$,and $BCl_{3}$ is ..... .