At `900^(@)C`, `pK_(w)` is 13. At this temperature an aqueous solution with `pH =7` will be

Options

A. Acid
B. Basic
C. Neutral
D. None of these

Answer

To solve the question, we need to analyze the given information about the pK_w and the pH of the solution at 900°C.

### Step-by-Step Solution:

1. **Understanding pK_w**:
At 900°C, the value of pK_w is given as 13. The ion product of water (K_w) can be calculated using the formula:
\[ K_w = 10^{-pK_w} = 10^{-13} \]

2. **Calculating pOH**:
The relationship between pH and pOH is given by the equation:
\[ pH + pOH = pK_w \]
Substituting the known values:
\[ 7 + pOH = 13 \]
Rearranging gives:
\[ pOH = 13 - 7 = 6 \]

3. **Finding the concentration of hydroxide ions**:
The concentration of hydroxide ions \([OH^-]\) can be calculated from pOH:
\[ [OH^-] = 10^{-pOH} = 10^{-6} \, \text{mol/L} \]

4. **Determining the nature of the solution**:
Since the pH of the solution is 7, which is less than the neutral pH at this temperature (which is 6.5, as derived from pK_w), the solution is considered to be acidic in nature.

### Final Answer:
At 900°C, an aqueous solution with pH = 7 will be **acidic** in nature.