P Block Elements

A $$\mathrel{\mathop{\kern0pt\longrightarrow} \limits_{}^{573\,K}}$$ Red phosphorus $$\mathrel{\mathop{\kern0pt\longrightarrow} \limits_{under\,pressure}^{heat\,;\,803\,K}}$$ B Red phosphorus is obtained by heating "A" at 573 K, and can be converted to "B" by heating at 803 K under pressure. A and B, respectively, are