Question

Which of the following statement(s) regarding allotropic forms of phosphorus is/are correct?

• A. White phosphorus is more reactive than red and black phosphorus due to high angular strain
• B. Red phosphorus on heating catches fire readily and gives dense red fumes of $P_4{0}_{10}$
• C. Red phosphorus is polymeric in nature consisting of chains of $P_4$ tetrahedra
• D. Black phosphorus has two forms $\alpha$-black and $\beta$-black phosphorus

Answer 1

Answer: (A), (C), (D)

Black phosphorus has two forms $\alpha$-black and $\beta$-black phosphorus

(a) The three allotropic forms of phosphorus differ widely in their chemical reactivity in which white phosphorus is the most reactive while black and red phosphorus are less reactive.
White phosphorus is made up of discrete $P_4$ tetrahedra which is subjected to very high angular strain as the angle is ${60}^{\circ }$. This high angular strain makes white phosphorus unstable and highly reactive.

(b) White phosphorus on heating catches fire readily and gives dense white fumes of $P_4{0}_{10}$. Unlike white phosphorus, red phosphorus does not ignite readily in air.​

(c) Red phosphorus is polymeric, consisting​ of chains of $P_4$ tetrahedra linked together, forming a giant molecule.

(d) Black phosphorus has two forms $\alpha$-black and $\beta$-black phosphorus.

Hence, option (a), (c) and (d) are correct.