Living beings carry out their metabolic activities in which of the following pH range?

7.0 to 7.8

The correct answer is option 2.  7.0 to 7.8

Living organisms can survive in a narrow range of pH levels for their metabolic activities. While some extremophiles can exist in more extreme conditions, the most common range for most organisms is 7.0 to 7.8

This is a slightly alkaline range, with a neutral pH being 7. Even small deviations from this range can disrupt enzyme activity and cellular processes, leading to malfunction and potentially death.

The other options you provided are not suitable for most life forms:

5.0 to 5.8: This is slightly acidic and can be tolerated by some acidophilic organisms (thriving in acidic environments) but not most life forms.

10.0 to 10.8: This is moderately alkaline and too basic for most organisms.

12.0 to 12.8: This is strongly alkaline and incompatible with life as we know it.