A noble gas with high fog-penetrating power used in aerodrome beacons is

Correct Answer: Krypton

Explanation:

• Krypton is a noble gas that produces an intense white light when electrically excited.
• Because of its high fog-penetrating power, it is particularly useful in aerodrome beacons and other signaling lights where visibility is poor.
• Other noble gases like neon and argon also emit light, but their visibility in fog is much lower compared to krypton.

Thus, the noble gas used in aerodrome beacons is Krypton.