Which of the following metals reacts directly with nitrogen to form a nitride?

Potassium permanganate,on heating,gives:

Nitrogen dioxide $(NO_2)$ cannot be obtained from the thermal decomposition of which of the following?

The correct statement$(s)$ among $I$ to $III$ with respect to potassium ions that are abundant within the cell fluids is/are :
$I.$ They activate many enzymes
$II.$ They participate in the oxidation of glucose to produce $ATP$
$III.$ Along with sodium ions,they are responsible for the transmission of nerve signals

Alkali metals in each period have

The catalyst used to convert sodium to sodium amide is