The reducing power of divalent species decreases in the order:

Options

A. `Ge gt Sn gt Pb`
B. `Sn gt Ge gt Pb`
C. `Pb gt Sn gt Ge`
D. None of these

Explanation

To determine the reducing power of divalent species in the order of their decreasing strength, we will analyze the elements in question: Lead (Pb), Tin (Sn), Germanium (Ge), and Silicon (Si).

### Step-by-Step Solution:

1. **Identify the Elements and Their Atomic Numbers**:
- Silicon (Si) - Atomic Number 14
- Germanium (Ge) - Atomic Number 32
- Tin (Sn) - Atomic Number 50
- Lead (Pb) - Atomic Number 82

2. **Understand the Concept of Reducing Power**:
- Reducing power refers to the ability of a species to donate electrons. The stronger the reducing agent, the more readily it can lose electrons.

3. **Consider the Atomic Structure**:
- As we move down the group from Si to Pb, the atomic number increases, which means more electron shells are added. This increases the distance of the outermost electrons from the nucleus, leading to a larger atomic radius.

4. **Evaluate the Screening Effect**:
- The screening effect occurs when inner shell electrons shield the outer electrons from the nucleus's positive charge. As we move down the group, the number of inner shell electrons increases, which reduces the effective nuclear charge felt by the outermost electrons.

5. **Inert Pair Effect**:
- In heavier elements like Pb and Sn, the inert pair effect becomes significant. The s-electrons (ns²) do not participate in bonding as effectively due to poor shielding by d and f electrons. This makes the +2 oxidation state more stable compared to the +4 state, which is less stable.

6. **Determine the Reducing Power Order**:
- Based on the above factors, the reducing power decreases in the order of Pb²⁺ > Sn²⁺ > Ge²⁺ > Si²⁺. This is because:
- Pb²⁺ has the highest reducing power due to its larger atomic size and the inert pair effect.
- Sn²⁺ follows as it is also a heavier element but less than Pb.
- Ge²⁺ has less reducing power than Sn²⁺.
- Si²⁺ has the least reducing power due to its smaller size and stronger effective nuclear charge.

### Final Order of Reducing Power:
**Pb²⁺ > Sn²⁺ > Ge²⁺ > Si²⁺**