$Fe(OH)_2$ is precipitated from $Fe(II)$ solutions as a white solid but turns dark green and then brown due to the formation of:

Potassium permanganate on heating at $513 \ K$ gives a product which is :

The colour of $K_2Cr_2O_7$ changes from red-orange to lemon-yellow on treatment with aqueous $KOH$ because of:

Which among the following statements is incorrect for interstitial compounds?
$1$. They are very hard and rigid
$2$. They have higher melting point than pure metal
$3$. They do not show conductivity
$4$. They are chemically inert

Which from the following alloys is used in gas turbine engines?

When dilute $H_2SO_4$ is added to an aqueous solution of potassium chromate,the yellow color of the solution turns to orange. What does this indicate?