Which isomer of $\mathrm{C}_4 \mathrm{H}_9 \mathrm{OH}$ has lower boiling point?

Which element from following in +2 state exhibits highest magnetic moment?

Which from following anions has maximum coagulating power for precipitation of positive sol?

What is the oxidation state of central metal ion in $\left[\mathrm{Fe}(\mathrm{CN})_6\right]^{4-}$ complex?