If $△\mathrm{ABC}\cong △\mathrm{PQR}$, then which of the following relation is true?

Two triangles are said to be congruent if the sides and angles of one triangle are equal to the corresponding sides and angles of the other triangle.

Given that, $△\mathrm{ABC}\cong △\mathrm{PQR}$

Therefore, by corresponding parts of congruent triangles,

$\mathrm{AB}=\mathrm{PQ}, \mathrm{BC}=\mathrm{QR}, \mathrm{CA}=\mathrm{RP}$

and $\angle \mathrm{A}=\angle \mathrm{P}, \angle \mathrm{B}=\angle \mathrm{Q}, \angle \mathrm{C}=\angle \mathrm{R}$

Hence, $\mathbf{\angle }\mathbf{A}\mathbf{=}\mathbf{\angle }\mathbf{P}$ is the correct alternative.