Correct Answer - C
The chromate and dichromate ions are in equilibrium and are inter-convertible by altering the pH of the solution.
`2CrO_(4)^(2-) +2H^(+) hArr2HCrO_(4)^(-)hArrCr_(2)O_(7)^(2-) +H_(2)O`
Upon the addition of an acid, the condentration of `H^(+)` increases. Hence, the equilibrium shifts in the forward direction accordance with
Le Chatelier priceiple forming `Cr_(2) O_(7)^(2-).` When a base `(OH^(-))` is added, the `H^(+)` ions are consumed and therefore, equilibrium shifts in the backward direction forming chromate ions
`(Cr _(2) O_(4)^(2-)).`
