( A ) $Na_2Cr_2O7$ is preferred over $ K_2Cr_2O_7$ in volumetric analysis
( B ) $K_2Cr_2O_7$ solution becomes yellow on increasing the pH beyond 7
( C ) On passing $H_2S$ through acidified $K_2Cr_2O_7$ solution, a milky colour is observed
( D ) $K_2Cr_2O_7$ solution in acidic medium is orange
