What is the punishment for a Muslim woman marrying a Christian, and how many times has this occurred and in which countries?

It is not permissible for a Muslim woman to marry a disbeliever (whether Jewish, Christian, or pagan), because a man has authority over a woman, and it is not permissible for a disbeliever to have authority over a Muslim woman. Furthermore, Islam is the religion of truth, and all others are false, as Allah Almighty says: (And do not marry polytheistic men [to your women] until they believe), and His saying: (And never will Allah grant the disbelievers a way [to triumph] over the believers), and the saying of the Prophet, peace and blessings be upon him: "Islam is exalted and nothing is exalted above it."

If a Muslim woman marries a disbeliever while aware of the ruling, she is an adulteress, and her punishment is the prescribed penalty for adultery (حد الزنا). If she is ignorant, she is excused, and a separation between them is obligatory without a divorce, due to the nullity of the marriage contract. Therefore, a Muslim woman and her guardian must beware of this.