When `20 mL` of `M//20NaOH` is added to `10mL` of `M//10 HCI`, the resulting solution will

Options

A. Turn blue litmus red.
B. Turn phenolpthalein solution pink.
C. Turns methy orange red.
D. Will have no effect on either red or blue litmus

Explanation

To solve the problem of what happens when `20 mL` of `M/20 NaOH` is added to `10 mL` of `M/10 HCl`, we can follow these steps:

### Step 1: Determine the Normality of NaOH and HCl
- **NaOH**: The concentration is `M/20`, which means the molarity is `1/20 M`. Since the n-factor (valence factor) of NaOH is `1`, the normality (N) is equal to the molarity (M).
- Normality of NaOH = `1/20 N` = `0.05 N`

- **HCl**: The concentration is `M/10`, which means the molarity is `1/10 M`. The n-factor of HCl is also `1`, so the normality is equal to the molarity.
- Normality of HCl = `1/10 N` = `0.1 N`

### Step 2: Calculate the Gram Equivalents of NaOH and HCl
- **Gram Equivalent of NaOH**:
\[ \text{Gram Equivalent of NaOH} = \text{Normality} \times \text{Volume (in L)} \]
\[ = 0.05 \, \text{N} \times \frac{20 \, \text{mL}}{1000} = 0.05 \times 0.02 = 0.001 \, \text{equivalents} \]

- **Gram Equivalent of HCl**:
\[ \text{Gram Equivalent of HCl} = \text{Normality} \times \text{Volume (in L)} \]
\[ = 0.1 \, \text{N} \times \frac{10 \, \text{mL}}{1000} = 0.1 \times 0.01 = 0.001 \, \text{equivalents} \]

### Step 3: Compare the Gram Equivalents
- Since the gram equivalents of NaOH and HCl are equal (0.001 equivalents each), this indicates that they will completely neutralize each other.

### Step 4: Determine the Resulting Solution
- The neutralization of NaOH and HCl results in a neutral solution. Therefore, the pH of the resulting solution will be `7` at `25°C`.

### Step 5: Effect on Litmus Paper
- A neutral solution will have no effect on either red or blue litmus paper. Red litmus will not turn blue, and blue litmus will not turn red.

### Conclusion
The resulting solution will have no effect on either red or blue litmus paper. Thus, the answer is option 4.

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