Which actinoid from the following has the smallest ionic size in the $+3$ oxidation state?

The percentage $(\%)$ of iron in pyrophoric mischmetal is ...........

Which of the following is responsible for the lanthanoid contraction?

What is the basic character of lanthanoid hydroxides?

Given below are two statements:
Statement $I$: $CeO_{2}$ can be used for the oxidation of aldehydes and ketones.
Statement $II$: Aqueous solution of $EuSO_{4}$ is a strong reducing agent.
In the light of the above statements,choose the correct answer from the options given below:

Explain lanthanoid contraction in detail. What is lanthanoid contraction? What are its consequences?