sends a frame of 1000 bytes, removes the frame after it has circulated all around the ring, and finally releases the token.
This signifies token passing technique used is DELAYED TOKEN REINSERTION( DTR )
In this case,
THT = Tt + RL = Tt + Tp + N*b
(In most cases, bit delay is 0)
So, THT = Tt + Tp [ RL = Tp ]
where Tt = transmission delay
Tp = propagation delay
Token Holding Time (THT) –The maximum time a token frame can be held by a station is known as THT.
No station can hold the token beyond THT.
Efficieny, e = Useful time/ Cycle time
useful time = N*Tt
cycle time = Tp + (THT*N)
N = no. of stations in ring
$\eta \ = \frac{N*T_t}{T_p +(THT*N)}$
N = 1 ( only 1 station is sending )
$T_t \ =\ 800 \mu s$
THT = (800 + 400)$\mu s$
$= 1200\mu s$
$\eta \ = \frac{1*800}{400 +(1200*1)}$
$\eta \ = \frac{800}{1600}$
$\eta \ = \frac{1}{2}$
BW = $\eta \ * R$
$= \frac{1}{2} \ *\ 10Mbps$
$= 5Mbps$
Answer: $C)$
Ref: https://www.geeksforgeeks.org/computer-network-efficiency-token-ring/