Light of frequency 1.5 times the threshold frequency is incident on...

${K}_{1} = 1 . 5h{v}_{0} - {ϕ}_{0} = 0 . 5h{v}_{0}$

${K}_{2} = 1 . 5h\dfrac{{v}_{0}}{2} - h{v}_{0} = - 0 . 25h{v}_{0}$

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

OR

In second case the incident frequency is halved
Incident frequency $= \dfrac{1 . 5}{2}{v}_{0} = 0 . 75{v}_{0}$
Now the incident frequency is less than threshold frequency, so no emission of electron take place therefore no current. $\left(i = 0\right)$