The bulbs are usually filled with which gases ?

The correct answer is (b).

Bulbs are usually filled with nitrogen and argon. Nitrogen is an inert gas that does not react with other substances, while argon is a noble gas that is also non-reactive. These gases help to prevent the formation of rust and other corrosion on the inside of the bulb, which can extend its lifespan.

Oxygen and hydrogen are both flammable gases, so they are not used in light bulbs. Helium is a lighter-than-air gas, so it is used in balloons and airships.

Here are some additional details about each of the options:

• Option (a): Oxygen and hydrogen are both flammable gases. If they were used in light bulbs, there would be a risk of fire.
• Option (b): Nitrogen and argon are both inert gases. They do not react with other substances, so they are safe to use in light bulbs.
• Option (c): Helium is a lighter-than-air gas. If it were used in light bulbs, the bulbs would float away.
• Option (d): Oxygen and argon are both inert gases. They do not react with other substances, so they are safe to use in light bulbs.