maihuna wrote:IMO : C

The and construction with... and surpass china..require to have a direct object....so the country will have 1.6B people and surpass china by 2050...seems to fit the bill...

About other option:

A: estimated as un-idiomatic
B: who they, Indians?
D:there fails the and test..and comparator as..
E ..same as above..

aj5105 wrote:The population of India has been steadily increasing for decades, and it will probably have what is estimated as 1.6 billion people by 2050 and surpass China as the world’s most populous nation.

A. it will probably have what is estimated as
it illogically refers to population of india

B. they are likely to have
same as above + they cannot refer to a nation

C. the country will probably have
Correct
D. there will probably be
plain BAD---> There where ?
E. there will be an estimated