My girl is 5 -year-old and has become too possessive about her things, she doesn't share any of her thing with anyone. How can I inculcate the quality of sharing in her?

Next time bring a chocolate and don't share it with her (just pretend) when she asks for a share. Tell her that it really feels bad when people don't share. Tell her about good and bad behavior. Tell her that sharing brings happiness to everyone's lives. Tell her stories about sharing.