The element that usually does NOT show variable oxidation states is :

For the cell Zn(s) |Zn²⁺ (aq)| |M^x+ (aq)| M(s), different half cells and their standard electrode potentials are given below :

Mx+ (aq)/M(s)	Au3+(aq)/Au(s)	Ag+(aq)/Ag(s)	Fe3+(aq)/Fe2+ (aq)	Fe2+(aq)/Fe(s)
E0Mx+/M/(V)	1.40	0.80	0.77	$$-$$0.44

If $$E_{z{n^{2 + }}/zn}^0$$ = $$-$$ 0.76 V, which cathode will give maximum value of E^o_cell per electron transferred?

The correct order of the atomic radii of C, Cs, Al, and S is :

A 10 mg effervescent tablet containing sodium bicarbonate and oxalic acid releases 0.25 ml of CO₂ at T = 298.15 K and p = 1 bar. If molar volume of CO₂ is 25.0 L under such condition, what is the percentage of sodium bicarbonate in each tablet ?
[Molar mass of NaHCO₃ = 84 g mol^–1]