Is this her dress?
Yes, it is.
What are these?
These are ...
These are ___ socks.
her
What is this?
This is ... / It is ...
Are these her trousers?
No, they aren't.
This is ___ dress.
her
Are these his shorts?
Yes, they are.
Is this his T-shirt?
No, it isn't.
This is ___ T-shirt.
his
What are these?
These are ...
What are these?
These are ...
What is this?
This is a ... / It is a ...