In the electrolytic refining of blister copper, the total number of main impurities, from the following, removed as anode mud is ______________

Pb, Sb, Se, Te, Ru, Ag, Au and Pt

The pH of a solution obtained by mixing 50 mL of 1 M HCl and 30 mL of 1 M NaOH is x $$\times$$ 10^$$-$$4. The value of x is ____________. (Nearest integer) [log 2.5 = 0.3979]

For the reaction A $$\to$$ B, the rate constant k(in s^$$-$$1) is given by

$${\log _{10}}k = 20.35 - {{(2.47 \times {{10}^3})} \over T}$$

The energy of activation in kJ mol^$$-$$1 is ____________. (Nearest integer) [Given : R = 8.314 J K^$$-$$1 mol^$$-$$1]

Sodium oxide reacts with water to produce sodium hydroxide. 20.0 g of sodium oxide is dissolved in 500 mL of water. Neglecting the change in volume, the concentration of the resulting NaOH solution is ______________ $$\times$$ 10^$$-$$1 M. (Nearest integer) [Atomic mass : Na = 23.0, O = 16.0, H = 1.0]