Using basic laws of kinematics :
h = 1/2 a t2 for an object relaesed from top which is initially at rest
So a = g for earth we can write :
t1 = sqrt (2h / g)
Now according to the question
acceleration due to gravity in TIFR planet = g / 2
So t2 = sqrt(4h / g) = sqrt(2) * sqrt (2h / g)
= sqrt(2) * t1 ..
Hence B) should be corrected answer..Only sqrt(2) should be there and 't' should be separate..Hence sqrt(2) * t is correct option..