The increasing order of basicity for the following intermediates is (from weak to strong)

The electronic configurations of bivalent europium and trivalent cerium are
(atomic number : Xe = 54, Ce = 58, Eu = 63)

How much amount of NaCl should be added to 600 g of water ($$\rho $$ = 1.00 g/mL) to decrease the freezing point of water to – 0.2 °C ? ______.
(The freezing point depression constant for water = 2K kg mol^–1)

The mass percentage of nitrogen in histamine is _____.