Let the distance covered by each of them be \( d \) km.
We are given that Mallya arrives 15 minutes before Malaraj. Converting 15 minutes into hours:
\[ 15 \text{ minutes} = \frac{15}{60} = \frac{1}{4} \text{ hours} \]
Thus, the equation becomes:
\[ \frac{d}{2} - \frac{d}{4} = \frac{1}{4} \]
Rewriting the equation:
\[ \frac{2d}{4} - \frac{d}{4} = \frac{1}{4} \]
\[ \frac{d}{4} = \frac{1}{4} \]
Multiplying both sides by 4:
\[ d = 1 \]
Thus, the distance covered by each of them is 1 km. The correct answer is (D) 1 km.