The correct answer is: C. 6%
Hydrogen evolved during charging produces explosive mixture when it is more than 6%.
The amount of hydrogen gas produced during charging depends on the type of battery, the charging rate, and the temperature. In general, the higher the charging rate, the more hydrogen gas is produced. The temperature also affects the amount of hydrogen gas produced, with higher temperatures producing more hydrogen gas.
The amount of hydrogen gas that can be safely present in the air is 4%. If the concentration of hydrogen gas in the air exceeds 4%, there is a risk of explosion.
Therefore, it is important to ensure that the amount of hydrogen gas produced during charging does not exceed 6%. This can be done by using a battery charger that is designed to control the charging rate and temperature. It is also important to ventilate the area where the battery is being charged.
Here is a brief explanation of each option:
- Option A: 2%. This is the lower limit of the safe concentration of hydrogen gas in the air. If the concentration of hydrogen gas in the air is below 2%, there is no risk of explosion.
- Option B: 4%. This is the maximum safe concentration of hydrogen gas in the air. If the concentration of hydrogen gas in the air exceeds 4%, there is a risk of explosion.
- Option C: 6%. This is the concentration of hydrogen gas at which an explosive mixture is produced. If the concentration of hydrogen gas in the air is more than 6%, there is a risk of explosion.
- Option D: 8%. This is the concentration of hydrogen gas at which an explosive mixture is highly likely to be produced. If the concentration of hydrogen gas in the air is more than 8%, there is a high risk of explosion.