Choose the correct statement.

Which compound forms double salt with sulphates of alkali metals?

Which compound is used in Ultra-violet calibration?

The main factor for the cause of lanthanide contraction is poorer shielding of 5d electrons by 4f electrons.

Which of the following element belongs to the first transition series of the periodic table?

What is the oxidation state exhibited by actinium?

Which of the actinoids is used in the treatment of cancer?

What is the general electronic configuration of the lanthanides?