A block of mass m is placed on a smooth inclined wedge ABC of...

In non-inertial frame of wedge

Using pseudo force,
Free body diagram is given as

Normal reaction is balanced by $mgcos\left(\theta\right)$

Where m is mass of the body,

g is the acceleration due to gravity

a is the acceleration produced by external force..
$macos \theta = mgsin \theta$

$a = \dfrac{gsin\left(\theta\right)}{\cos \left(\theta\right)}$

$a = gtan \theta$