C. 2 hr 30 min
Feedback A tap can fill a tank in 4 hours.
Therefore the tap can fill half the tank in 2 hours.
Remaining part =1/2
After half the tank is filled, three more similar taps are opened.
Hence, total number of taps becomes 4.
Part filled by one tap in 1 hour =1/4
Part filled by four taps in 1 hour =4×1/4=1i.e., 4 taps can fill remaining half in 30 minutes.
Total time taken= 2 hour + 30 minute = 2 hour 30 minutes