To solve the given question, we need to analyze both statements and determine their validity.
### Step 1: Analyze Statement 1
**Statement 1:** The pH of `10^(-7)` M HCl is less than 7 at `25°C`.
- At `25°C`, the pH of pure water is 7, which corresponds to a hydrogen ion concentration of `10^(-7)` M.
- When we add `10^(-7)` M HCl, it dissociates completely into `H^+` and `Cl^-`, contributing an additional `10^(-7)` M of `H^+`.
- Therefore, the total concentration of `H^+` ions becomes:
\[
[H^+] = 10^{-7} \, \text{M (from HCl)} + 10^{-7} \, \text{M (from water)} = 2 \times 10^{-7} \, \text{M}
\]
- The pH is calculated as:
\[
\text{pH} = -\log(2 \times 10^{-7}) = -\log(2) - \log(10^{-7}) = 7 - 0.301 = 6.699
\]
- Since the pH is approximately 6.70, which is less than 7, **Statement 1 is true**.
### Step 2: Analyze Statement 2
**Statement 2:** At very low concentration of HCl, the contribution of `H^+` from water is considerable.
- At low concentrations, the contribution of `H^+` ions from the dissociation of water (`10^{-7}` M) becomes significant compared to the `H^+` ions from HCl.
- In this case, the total `H^+` concentration must consider both contributions:
\[
[H^+] = [H^+]_{HCl} + [H^+]_{H_2O}
\]
- Hence, at very low concentrations of HCl, the contribution from water cannot be neglected, making **Statement 2 true**.
### Step 3: Determine the Relationship Between Statements
- Since both statements are true and Statement 2 provides a correct explanation for Statement 1, we conclude that the correct option is:
- **Option 1:** Statement 1 is true, Statement 2 is true, and Statement 2 is the correct explanation for Statement 1.
### Final Answer
The answer is **Option 1**.
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