Which of the following statements is true about the `14^(th)` group elements ?

Options

A. a. The stability of their dihalides increases steadily in the order `:PbX_(2) lt SnX_(2) lt GeX_(2) lt SiX_(2)`.
B. b. The tendency of the elements to catenation decreases as `C gt Si gt Ge ~~ Sn gt Pb`
C. c. Both `[SiF_(6)]^(2-)` and `[SiCl_(6)]^(2-)` are known.
D. d. Silica is inert towards `NaOH` but it is attacked by HF forming `SiF_(4)`.

Explanation

To determine which statement is true about the 14th group elements, we will analyze the provided options step by step.

### Step 1: Identify the Elements in Group 14
The 14th group elements (also known as Group IV) in the periodic table are:
- Carbon (C)
- Silicon (Si)
- Germanium (Ge)
- Tin (Sn)
- Lead (Pb)

### Step 2: Analyze Each Statement
We will evaluate each statement provided in the question to find the correct one.

#### Statement A: Stability of their dihalides increases steadily
- The dihalides of the group 14 elements can be represented as MX₂, where M is the group element and X is a halogen.
- The stability of dihalides generally decreases down the group due to the inert pair effect. The order of stability is typically PbX₂ < SnX₂ < GeX₂ < SiX₂ < CX₂.
- Therefore, this statement is **incorrect**.

#### Statement B: Tendency of elements to catenation decreases
- Catenation refers to the ability of an element to form chains or rings by bonding to itself.
- The bond enthalpy for C-C is higher than for Si-Si, Ge-Ge, Sn-Sn, and Pb-Pb.
- The order of bond strengths is C-C (348 kJ/mol) > Si-Si (297 kJ/mol) > Ge-Ge (260 kJ/mol) > Sn-Sn (240 kJ/mol) > Pb-Pb (less than Sn).
- This indicates that the tendency to catenate decreases down the group, making this statement **correct**.

#### Statement C: Existence of SiF₆²⁻ and SiCl₆²⁻
- SiF₆²⁻ is known to exist, but SiCl₆²⁻ does not exist due to the larger size of Cl compared to F, which affects the stability of the complex.
- Therefore, this statement is **incorrect**.

#### Statement D: Silica is inert towards NaOH
- Silica (SiO₂) does react with NaOH under certain conditions to form silicates. Therefore, it is not inert towards NaOH.
- This statement is also **incorrect**.

### Conclusion
After evaluating all the statements, the only true statement about the 14th group elements is **Statement B**: "The tendency of elements to catenation decreases."