Nitrogen forms N_2, but phosphorus is converted into P_4 from P, the reason is

Correct answer is (a) a biological process of nitrogen fixing bacteria present in soil 

(b) calcium and phosphorus

[Hint : Because it have polymeric structure consisting chains of P4 tetrahedra, hence denser than white P while red P is not having angular strain as in white P, hence...

[Hint : (i) 4 (ii) Because due to presence of vacant d-orbitals in the octet of 'p', it can expand its octet to form PCl5, while N cannot expand its octet.]

(a) : 7N = 1s2 2s2 3p3 15P = 1s2 2s2 2p6 3s2 3p3 In phosphorus the 3dorbitals are available.

(c) both concave and convex mirror

(c) Assertion is correct, reason is incorrect 

 (b) White phosphorus exists as P4 tetrahedral molecule having P-P-P bond angle 60º. Hence the molecule is under strain and more reactive. On the other hand red phosphorus exists as...

(B)If both assertion and reason are true, but reason is not the true explanation of the assertion.

(a) when fossil fuels are burned at high combustion temperatures.