Is it true that if a ritually impure, or a menstruating woman visits one who is in confinement, harm will be inflicted on the latter, or her baby?

This is completely wrong and unfounded piece of information.

Should the Zakah (obligatory charity) giver tell the poor recipient that this is the Zakah of his money?

No, he shouldn`t. But, the Zakah giver should make an intention in his heart that it is the Zakah of his money when paying it to the poor. And Allah Knows Best.

How does a praying person prostrate?

All perfect praise be to Allah,The Lord of The Worlds                                                                                                                                                                        It is from Sunnah that he/she sits with both knees on the ground in order to prostrate, then hands, nose and forehead are placed on the same place. In addition, the toes have to touch the ground, and be directed towards the Qiblah (direction of Ka`bah) during prostration. And Allah Knows Best.

What is the ruling on combining prayers at the Musala (Place for prayer) of a shopping center because of heavy rain, knowing that some people come from outside that center?

Praise be to Allah, the Lord of the Worlds.

If there is hardship in going back to that Musala at the time of Asr or Isha` prayers, then it is permissible to combine prayers in twos only (Duhr with Asr and Maghrib with Isha`). Kindly consider calling us. And Allah Knows Best.