A paternal uncle as a Mahram

Q 1: Is it permissible for the paternal or maternal uncle to look at the face of his niece? Is it permissible for the niece to shake hands with or greet her paternal or maternal uncle? Since I have no knowledge about this matter, please answer me and substantiate your answer with evidence from the Qur'an and the Sunnah (whatever is reported from the Prophet).

A: The uncle, whether paternal or maternal, is regarded as a Mahram (unmarriageable relative) to his niece. He, therefore, is allowed to see of her what the other Mahrams are permitted to see. May Allah grant us success. May peace and blessings of Allah be upon our Prophet Muhammad, his family and Companions.