Time period of a pendulum is inversely proportional to the square root of acceration due to gravity.
T α 1/√g
given that gravity falls to one-fourth.
g' = g/4
let original time period = T
final time period = T'
So the time period becomes 2 times
the original time period.
Time period of a seconds' pendulum = 2s
New Time period = 2×2s = 4s