Which of the following is a radio isotope of the hydrogen?

Tritium

The correct answer is option 4. Tritium.

The radioisotope of hydrogen is Tritium.

Tritium is an isotope of hydrogen with two neutrons in its nucleus, in addition to the usual proton. Its symbol is \(^3_1H\), indicating one proton and two neutrons.

Xenon, technetium, and thorium are not isotopes of hydrogen; they are different elements or isotopes of other elements.