Consider the following statements ,
`(I)` Amongst `HCl,HBr,HI` and `HOCl,HCl` is most stable to heat.
`(II)` Chlorine gas if evolved when potassium chloride reacts with iodine.
`(III)` The basicity of `F^(-),Cl^(-),Br^(-)` , and `I^(-)` follows the order `F^(-)gt Cl^(-) gtBr^(-) gtI^(-)`
`(IV)` Sodium hypochlorite is used as bleaching and sterilising agent of these,

Explanation

To analyze the given statements, we will evaluate each one step by step.

### Step 1: Evaluate Statement I
**Statement I:** Amongst HCl, HBr, HI, and HOCl, HCl is most stable to heat.

- **Analysis:** The thermal stability of hydrogen halides (HX) decreases as we move down the group in the periodic table. This is due to the weakening of the H-X bond strength as the size of the halogen increases. Since HCl has a stronger bond compared to HBr and HI, it is indeed the most stable towards heat.

**Conclusion:** Statement I is **True**.

### Step 2: Evaluate Statement II
**Statement II:** Chlorine gas is evolved when potassium chloride reacts with iodine.

- **Analysis:** The reaction between potassium chloride (KCl) and iodine (I2) does not produce chlorine gas (Cl2). Instead, chlorine has a higher electron gain enthalpy than iodine, which means chlorine is more stable and cannot be displaced by iodine. The reverse reaction, where Cl2 reacts with potassium iodide (KI) to produce KCl and iodine, is feasible. Thus, the statement is incorrect.

**Conclusion:** Statement II is **False**.

### Step 3: Evaluate Statement III
**Statement III:** The basicity of F^(-), Cl^(-), Br^(-), and I^(-) follows the order F^(-) > Cl^(-) > Br^(-) > I^(-).

- **Analysis:** Basicity of halide ions decreases down the group due to the increase in atomic size and decrease in charge density. Fluoride (F^-) has the highest charge density and thus the highest basicity, while iodide (I^-) has the lowest. Therefore, the order given in the statement is correct.

**Conclusion:** Statement III is **True**.

### Step 4: Evaluate Statement IV
**Statement IV:** Sodium hypochlorite is used as a bleaching and sterilizing agent.

- **Analysis:** Sodium hypochlorite (NaOCl) is indeed used as a bleaching agent and a sterilizing agent. Upon gentle heating, it decomposes to produce sodium chloride and nascent oxygen, which is a powerful oxidizing agent. This property makes it effective for bleaching and sterilizing.

**Conclusion:** Statement IV is **True**.

### Final Conclusion
Based on the evaluations:
- Statement I: True
- Statement II: False
- Statement III: True
- Statement IV: True

The correct statements are I, III, and IV. Therefore, the answer is option C.

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