"Neha is writing a book."

Translation: नेहा किताब लिख रही है ।

[paul376479]

And why not 'eck' to denote a single book? Neha eck kitab lik rahi hai. ?

[SyedaAbeeha]

This is as the meaning is clear. It is known to us that she is writing 1 book. And also here kitaab is given in singular so it is known.