Extraction of metal from the ore cassiterite involves

The maximum number of electrons that can have principal quantum number, n = 3, and spin quantum number, m_s = − 1/2 , is

The work function ( φ ) of some metals is listed below. The number of metals which will show photoelectric effect when light of 300 nm wavelength falls on the metal is

The difference in the oxidation numbers of the two types of sulphur atoms in Na₂S₄O₆ is