A → 573 K Red phosphorus →[ under pressure ] heat; 803 K B Red phosphorus is obtained by heating "A" at 573 K, and can be converted to "B" by heating…

$\displaystyle A \xrightarrow{573 \mathrm{~K}}$ Red phosphorus $\displaystyle \xrightarrow[\text { under pressure }]{\text { heat } ; 803 \mathrm{~K}} B$ Red phosphorus is obtained by heating "A" at $\displaystyle 573$ K, and can be converted to "B" by heating at $\displaystyle 803$ K under pressure. A and B, respectively, are