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. $H_{3}P{O}_2$

2. $H_{3}P{O}_3$

3. $H_{3}P{O}_4$

4. $H_4{P}_2{O}_7$

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