Income tax return filing compulsory for foregin national

Dear Sir,

Please can you please guide me regarding "Income Tax Return Filing Compulsory for Foregin national" .

If Foregeiner working in India and he erned the Income from INdia then liable to File Income Tax Return?

if his/her salary less then 250,000/- i.e. Income Tax Limit then liable to file INcome Tax Return?

what is Critetia for Foregeiner of Income Tax Return Filing?

Thanking you in advance.

Reagrds
Rajnish