This is a simple and straightforward question on Relative Speed.
Relative Speed is the speed of two objects which are moving simultaneously. It is calculated as the sum of the speeds when both objects are moving in opposite directions, and, as the difference of the speeds when both objects are moving in the same directions.
In this question, the leopard and the deer are moving in the same direction. So, the relative speed will be the difference of their speeds.
Relative Speed = 12 – 10 = 2 km/h.
This means that the leopard will gain 2 km over the deer, in every one hour. Or, in other words, the deer will lose 2 km to the leopard, in every one hour.
When the leopard perceived the deer, the distance it had to gain was 200 metres i.e. 0.2 km. This means, it will take the leopard \((\frac{0.2}{2})\) hours \((\frac{distance}{relative speed})\) to catch the deer.
Since both the leopard and the deer started running at the same time and ended running at the same time (leopard catching the deer), we may say that both ran for a period of \((\frac{1}{10})\) hours.
In \((\frac{1}{10})\) hours, the deer can run 10 * \((\frac{1}{10})\) = 1 km.
The correct answer option is A.
Hope this helps!