To find the missing number that makes the fractions equal, we can set up the equation:
\[ \frac{2}{x} = \frac{1}{4} \]
Next, we can cross-multiply:
\[ 2 \cdot 4 = 1 \cdot x \]
This simplifies to:
\[ 8 = x \]
So, the missing number is \( \boxed{8} \).