Lanthanoid contraction is caused due to an increase in . . . . . . .

Which material is used in the flint of a gas lighter?

Which of the following lanthanoids exhibits no effective magnetic moment in the $+3$ oxidation state?

Knowing that the chemistry of lanthanoids $(Ln)$ is dominated by its $+3$ oxidation state,which of the following statements is incorrect?

Choose the correct option regarding the following.
Assertion: Actinides exhibit a larger number of oxidation states than lanthanides.
Reason: There is a large energy gap between $5f$,$6d$ and $7s$ sub-shells.

On the basis of Lanthanoid contraction,explain the following :
$(i)$ Nature of bonding in $La_2O_3$ and $Lu_2O_3$.
$(ii)$ Trends in the stability of oxo salts of lanthanoids from $La$ to $Lu$.
$(iii)$ Stability of the complexes of lanthanoids.
$(iv)$ Radii of $4d$ and $5d$-block elements.
$(v)$ Trends in acidic character of lanthanoid oxides.