Question

White phosphorus burns in a limited supply of air to form a soft white solid. This solid is Phosphorus __.

Answer 1

When $P_4$ is burnt in a limited supply of $O_2$,
$P_4\left(s\right)+3O_2\left(g\right)\to P_4{O}_6\left(s\right)$

The product, a soft white solid, is removed from the reaction mixture and is purified using distillation.