Question

Orange solution of potassium dichromate turns yellow on adding sodium hydroxide to it. Give reason.

Answer 1

Actually, the orange coloured potassium dichromate solution is when treated with basic NaOH solution, it is converted to chromate which gets a faint coloured like yellow.
The reaction is given as:
$K_{2}C{r}_2{O}_7+H_{2}S{O}_4$ --> $K_{2}Cr{O}_4+N{a}_{2}Cr{O}_4+H_{2}O$

This formation of chromate ($Cr{O}_4^2-$) ion converts the colour of the solution to yellow.