Is it permissible to place a divider between men and women in the mosque, and is it permissible for a non-hijabi woman to enter the mosque and attend a lesson given to men, and is it obligatory for a woman who wishes to enter the mosque to wear a hijab?

It is permissible to place a divider between men and women in the mosque to prevent temptation (fitnah) and to provide comfort for the worshipers. If there is no divider, then women should stand in their rows behind the men's rows. A Muslim woman must not leave her home or appear before non-mahram men except with a complete, legitimate hijab. This is a condition for the validity of prayer, and it must cover the tops of her feet and include a head covering (khimar) that she wraps around herself. There is no objection to a woman giving a lesson in the mosque or elsewhere if it adheres to the legitimate Islamic guidelines, and it is preferable for it to be in the area designated for women.