Transition elements with lower oxidation states act as........

Which of the following ions can reduce dilute acid to give hydrogen gas?

When $Cu^{2+}$ ion is treated with $KI$,a white precipitate is formed. Explain the reaction with the help of a chemical equation.

Discuss the chemical properties of lanthanoids.

The set of correct statements is:
$(i)$ Manganese exhibits $+7$ oxidation state in its oxide.
$(ii)$ Ruthenium and Osmium exhibit $+8$ oxidation state in their oxides.
$(iii)$ $Sc$ shows $+4$ oxidation state which is oxidizing in nature.
$(iv)$ $Cr$ shows oxidizing nature in $+6$ oxidation state.

All $Cu(II)$ halides are known except $CuI_2$,because ....