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 $X = F, Cl, Br, I$):
$2Ln + 3X_2 \rightarrow 2LnX_3$

When $KI$ and $CuSO_4$ solutions are mixed,the products formed are:

The correct order of basicity of oxides of vanadium is

All $Cu(II)$ halides are known,except the iodide. The reason for this is that:

Which of the following are amphoteric oxides?
$Mn_2O_7, CrO_3, Cr_2O_3, CrO, V_2O_5, V_2O_4$

Given below are two statements for catalytic properties of transition metals. Statement $I$: First row transition metals which act as catalyst utilise their $3d$ electrons only for formation of bonds between reactant molecules and atoms on the surface of catalyst. Statement $II$: There is increase in the concentration of reactants on the surface of catalyst which strengthens the bonds in reacting molecules. In the light of the above statements, choose the correct answer from the options given below: