The correct answer is A. 28.49 m.
The curve lead is the distance from the point of intersection of the two tracks to the point where the flange of the wheel of a vehicle on the diverging track first touches the inside rail of the main track. It is necessary to provide a curve lead to ensure that the wheels of the vehicle do not derail as it enters the turnout.
The curve lead for a 1 in 8.5 turnout taking off from a straight broad gauge track is given by the following formula:
$L = \frac{25}{8.5} \times 1000 = 28.49 \text{ m}$
where $L$ is the curve lead in metres and $1000$ is the conversion factor from millimetres to metres.
Option B is incorrect because it is the curve lead for a 1 in 10 turnout. Option C is
incorrect because it is the curve lead for a 1 in 12 turnout. Option D is incorrect because it is the curve lead for a 1 in 15 turnout.