The correct option is A 1
Given expression 2100−299−298……−22−21−20
=299(2−1)−298−297……22−21−20
=299−298−297……−22−21−20
=298(2−1)−297……−22−21−20
=298−297……−22−21−20
=297−296……−22−21−20
Continuing this process until the final step, we get
=23−22−21−20
=22−21−20
=21−20
=2−1=1
Hence, the value of the given expression is =1