c
\(\begin{array}{l}
\,\,\,\,\,\,\,\,\,\,In\,non - inertial\,frame,\\
N\sin \theta  = ma\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,...\left( i \right)\\
N\cos \theta  = mg\,\,\,\,\,\,\,\,\,\,\,\,\,...\left( {ii} \right)\\
From\,\left( i \right)\,and\,\left( {ii} \right),\\
\tan \theta  = \frac{a}{g} \Rightarrow a = g\tan \theta 
\end{array}\)