The correct option is C 10 masons
A wall is built in 2 days by 5 masons.
We know that the lesser the number of days to build, more will be the number of masons required.
So, Number of days(x) ∝1Number of masons(y)
∴x1x2 = y2y1
x1 = 2 days
y1 = 5 masons
x2 = 1 day
and y2 = number of masons required
⇒ y2 = 2 × 51 = 10 masons
∴ 10 masons should be employed to build a wall in a single day.