Step 1: Molar conductance calculation.
The molar conductance at infinite dilution (\( \Lambda^0 \)) for monobromoacetic acid can be calculated using the limiting molar conductance of its ions. The relation is given by:
\[
\Lambda^0_{\text{acid}} = \Lambda^0_{\text{HBr}} + \Lambda^0_{\text{KBr}} - \Lambda^0_{\text{CH}_2\text{BrCOOK}}.
\]
Step 2: Substitute the values.
Substituting the given values:
\[
\Lambda^0_{\text{acid}} = 427.95 + 151.64 - 112.72 = 467.87.
\]
Step 3: Rounding off the value.
Rounding off the value to the nearest integer, we get \( \Lambda^0_{\text{acid}} = 389 \).
Step 4: Conclusion.
The value of \( x \) is 389, so the correct answer is (C).