Mixture (s) showing positive deviation from Raoult’s law at 35^oC is (are)

For the following electrochemical cell at 298 K
Pt(s) | H₂ (g, 1 bar) | H⁺ (aq, 1 M) || M⁴⁺ (aq), M²⁺ (aq) | Pt (s)
E_cell = 0.092 V when $${{\left[ {{M^{2 + }}(aq)} \right]} \over {\left[ {{M^{4 + }}(aq)} \right]}}$$ = 10^x
Give, $$E_{{M^{4 - }}/{M^{2 + }}}^o$$ = 0.151 V; 2.303 RT/F = 0.059 V

The value of x is

Extraction of copper from copper pyrite (CuFeS₂) involves

The correct order of acidity for the following compounds is