the substance which allows heat radiations to pass through is.a)iron b)water vapour c)wood d)dry air

The substance that allows heat radiation to pass through is dry air, option d.

Explanation: Heat radiation is a form of energy transfer that occurs through electromagnetic waves. It does not require a medium, such as air or a solid, to travel. However, different substances can have varying effects on heat radiation.

In this case, dry air refers to air that does not contain any significant amount of water vapor. Dry air allows heat radiation to pass through because it has low absorption and low emission characteristics for thermal radiation. In other words, air molecules do not absorb and re-emit heat radiation as much as other substances like water vapor, wood, or iron.

Iron (option a) is a good conductor of heat, but it does not readily allow heat radiation to pass through. Water vapor (option b) and wood (option c) have higher absorption and emission properties for heat radiation, making them less effective at allowing it to pass through compared to dry air.

Therefore, the correct answer is d) dry air.

D. Dry air