Question

Wheatstone bridge is the most sensitive when all the four resistances are of the same order of magnitude.

Answer 1

Wheatstone bridge is actually a device which is used to find the unknown resistance when other 3 resistances out of 4 are known.

Yes it is true that Wheatstone bridge is more sensitive when all 4 resistances are of same order as the galvanometer shows null deflection at mid point hence this shows all the 4 resistances are of same order

P/Q = R/S

Their ratio will give the value of unknown resistance .