Oxidation number of P in pyrophosphoric acid is:
1. +5
2. +2
3. +3
4. +4

A compound having two direct bonds between P and H atoms is:

1. \(\mathrm{H}_3 \mathrm{PO}_2\)${\mathrm{}}_{}$

2. \(\mathrm{H}_3 \mathrm{PO}_3\)${}_{}$

3. \(\mathrm{H}_3 \mathrm{PO}_4\)${}_{}$

4. \(\mathrm{H}_4 \mathrm{P}_2 \mathrm{O}_7\)${}_{}$

Find the reason why nitrogen exists as N₂, whereas phosphorus exists as P₄.

1. Presence of a triple bond between phosphorus atoms
2. $\mathrm{Weak\; p\pi –p\pi \; bonding\; in\; phosphorus}$

3. $\mathrm{Strong\; p\pi –p\pi \; bonding\; in\; phosphorus}$
 
4. Multiple bonds easily form in phosphorus