Which one of the following sulphides is yellow?

Which of the following melts in boiling water?

Fill in the blanks:
$(1)$ ......... acid is added to perform titrations with $KMnO_4$ and $K_2Cr_2O_7$.
$(2)$ Crystals of potassium dichromate are of ......... color,while crystals of potassium chromate are of ......... color.
$(3)$ The color of $MnO_4^{2-}$ is ......... and the color of $MnO_4^-$ is ......... .

Which of the following is incorrect about $K_{2}Cr_{2}O_{7}$?

$2KMnO_4 \xrightarrow{200^{\circ}C} K_2MnO_4 + MnO_2 + O_2$. Here,'$X$' is $K_2MnO_4$. Which of the following statements is correct for '$X$'?

$ \uparrow Y_{(g)} \xleftarrow{KI} CuSO_4 \xrightarrow{dil. H_2SO_4} X (\text{Blue colour}) $. $X$ and $Y$ are: