Oxygen is absorbed by molten $Ag$,which is evolved on cooling and the silver particles are scattered,this phenomenon is known as

Ferrous sulphate on heating gives

Identify the correct statement.

Which of the following pairs of compounds do not exist?

The copper $(II)$ halide which does not exist is:

Write the chemical reactions of lanthanoids $(Ln)$ with the following:
$(1)$ With acid:
$2Ln + 6HCl \rightarrow 2LnCl_3 + 3H_2$
$(2)$ With halogens ($X_2$,where $X = F, Cl, Br, I$):
$2Ln + 3X_2 \rightarrow 2LnX_3$