25 ml of the given HCl solution requires 30 mL of 0.1 M sodium carbonate solution. What is the volume of this HCl solution required to titrate 30 mL of 0.2 M aqueous NaOH solutions ?

The de Broglie wavelength ($$\lambda $$) associated with a photoelectron varies with the frequency (v) of the incident radiation as, [v₀ is threshold frequency] :

The reaction, MgO(s) + C(s) $$ \to $$ Mg(s) + CO(g), for which $$\Delta $$_rH^o + 491.1 kJ mol^–1 and $$\Delta $$_rS^o = 198.0 JK^–1 mol^–1, is not feasible at 298 K. Temperature above which reaciton will be feasible is :

K₂Hgl₄ is 40% ionised in aqueous solution. The value of its van't Hoff factor (i) is: