Which compound of zinc is white in the cold state and turns yellow in the hot state?

Fill in the blanks:
$(1)$ In the dichromate ion,the $O-Cr-O$ bond angle is ....... $^o$.
$(2)$ The reaction $3Sn^{2+} \to 3Sn^{4+} + 6e^-$ occurs via .........,in which $Sn^{2+}$ is ......... .
$(3)$ The symbols for stannous and stannic are ......... and ......... respectively.
$(4)$ $V_2O_4$ dissolves in acidic compounds to give ......... salts.

Which one of the following species is stable in aqueous solution?

Copper sulphate is not used:

What is the composition of the alloy that exhibits the property of shape memory?

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