he is grateful to his master  -------------------------- many favours.

he is grateful to his master in many favours

he is grateful to his master for many favours

 He is grateful to his master FOR many favours. 

He is grateful to his  master for many favours...

   for 

for 

oblidging

IN

in and for both are correct ,and both have different meanings

if in is used it gives meaning  that  the person is helping his master in many things

if for is used then it gives meaning that the person's master helped him in many things hence he is favourable to him.

 in and for both are correct ,and both have different meanings

if in is used it gives meaning that the person is helping his master in many things

if for is used then it gives meaning that the person 's master helped him in many things hence he is favourable to him.

 for.

 for

He is grateful to his master  in  many favors.

He is grateful to his master for  many favors.

For

FOR !

for

He is grateful to his master for his many favours.