Transition metal with low oxidation number will act as

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

Transition metals vary widely in their chemical reactivity. Explain this with examples or write about the reactivity of $3d$ series metals with acids.

The order of basic character for the monoxides of transition metals is . . . . .

The catalytic activity of transition metals and their compounds is ascribed mainly to

$\underset{\text{coloured}}{P(\text{soln.})}$ $\xrightarrow{\text{Air}} \underset{\text{coloured}}{Q(\text{soln.})}$ $\xrightarrow{KOH} R \downarrow$
$(R = \text{ppt. Insoluble in both excess } NaOH \text{ and excess } NH_3 \text{ solution})$
Then $P$ contains