( H T )_ P is the mathematical expression for

Answer: Option D

By the definition of $$C_P$$ we can write $$C_P=\underset{\delta T\to 0}{\lim }{\left(\frac{\delta Q}{\delta T}\right)}_P.$$
Under constant pressure process and by first law of thermodynamics
$$\begin{array}{rl}& Q=dH\\ & \Rightarrow {\left(\frac{\partial H}{\partial T}\right)}_P=C_P.\end{array}$$