Class 12th

31. Option (i)

Below point A, only the value of ΔG (CO, CO₂) is less than the value of ΔG (Fe, FeO) at the corresponding temperatures. Thus, only carbon monoxide will be able to reduce FeO to Fe and will get itself oxidized into CO₂.

30. Option (iv)

Above point A, ΔG (C, CO)

29. Option (i) 

The cyanide process involves 3 steps:

First step - The finely grounded ore of gold and silver are made to come in contact with the solution containing the cyanide,

Second step - it involves separation of gold and silver from the cyanide solution  

Third step - it involves the recovery of gold and silver in their pure forms precipitating the remaining solution with zinc dust.

Thus, the metal is recovered by displacing Zn with the metal (Au or Ag) from metal ions.

28. Option (i)

The electrolytic method can be used to purify zinc and copper. The impure metal is used as an anode in this method. As the cathode, a pure strip of the same metal is used. They are immersed in an appropriate electrolytic bath containing a soluble salt of the same metal.

The more basic metals remain in the solution, while the less basic metals are transferred to the anode mud.

27. Option (ii)

Reaction involved in the metallurgy of aluminum is 2Al₂O₃ + 3C→ 4Al + 3CO₂.

The reaction at cathode is Al³⁺ + 3e⁻→ Al

The reaction at anode is

C+12O₂ →CO + 2e and C+O₂→CO₂ + 4e⁻

Hence, from the reaction graphite anode is oxidized to carbon monoxide and carbon dioxide.

10. Mn has half-filled 3d⁵ electrons and Zn has fully-filled 3d¹⁰ electrons which give them extra stability and they both resist to lose electrons and get reduced. 

The E? value also depends on the hydration enthalpy. More negative is the enthalpy of hydration, high is the E? value. This is the reason behind Mn, Ni and Zn are having higher E? value than expected

26. Correct option (i)

The reaction at the anode with a lower E $°$  value is preferred, but oxygen cannot be obtained in this process due to overvoltage.

9. Copper lies below hydrogen in electrochemical series which means it has positive standard reduction potential i.e.   + 0.34 V. and hence cannot liberate hydrogen from acids.

25. Option (iii)

Reaction takes place as Cu₂O + $\frac{1}{2}$ Cu₂S?3Cu +12SO₂ with a product as bristle copper. This type of reaction is called an auto-reduction reaction as copper is reducing itself with help of other copper compounds.