Correct answer is (a) Qp = C1. A^2/3
For explanation I would say: All tank weirs generally in South India are designed on the basis of Ryve’s formula which is given by:
Qp = C1.A^2/3 where Qp is the peak flood discharge, C1 is the Ryve’s coefficient, A is the catchment area
The formula is directly applicable for free catchments in all isolated tanks.