Mongo DB Replica set - not able to read also
The reason

The answer is quite simple: when two voting nodes of three are down, the remaining one reverts to secondary, to which – by definition – one can't write. The default read preference is to read from and write to the primary of a replica set only. Hence, when only a secondary remains in the replica set, you can not read.

tl;dr

You have to change your read preference at least to primaryPreferred, allowing reads from secondaries.