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

Which of the following pairs exhibit color in aqueous medium?

Fill in the blanks:
$(a)$ The ground state electronic configurations of $Cr$ and $Cu$ are .......... and ..........,respectively.
$(b)$ Transition elements exhibit certain characteristic properties due to partially filled $d$-orbitals.
$(c)$ The general electronic configuration of transition elements is .......... .

What are the characteristics of the transition elements and why are they called transition elements? Which of the $d$-block elements may not be regarded as the transition elements?

The halides of transition elements become more covalent with increasing oxidation state of the metal. Why?

Which of the following is a colourless ion?