$K_1=1.5 h{v}_0-{\varphi }_0=0.5 h{v}_0$

$K_2=1.5h\frac{v_0}{2}-h{v}_0=-0.25 h{v}_0$

$\because$ Kinetic energy can never be negative so, no emission and $i=0$

OR

In second case the incident frequency is halved
Incident frequency $=\frac{1.5}{2}{v}_0=0.75 v_0$
Now the incident frequency is less than threshold frequency, so no emission of electron take place therefore no current. $\left(i=0\right)$