Explanation

Tetrafluoroethane (HFC-134a) is commonly used in modern refrigerators.

Unlike Freon, it does not deplete the ozone layer.

Explanation

In January, Pakistan retaliated against Iran following a border clash.

This incident was part of ongoing tensions along the Pakistan-Iran border.

Explanation

Explanation

"May I come in?".

This is used when requesting permission to enter a place.

Explanation

Optics is the branch of physics that studies light and its interactions with matter.

It including phenomena such as reflection, refraction, and dispersion.

Explanation

Sudan split into two countries in 2011, with South Sudan becoming an independent nation.

This separation followed decades of conflict and a referendum in which South Sudan voted for independence.