For measuring energy status of soils water, tensiometer works well within moisture range upto:

Correct option is A

A tensiometer is a device used to measure the matric potential (or tension) of water in soils, indicating how tightly water is held by soil particles.
Tensiometers are most effective at low tension levels, specifically up to about 0.8 bars (or 80 centibars).
Beyond this range, the soil becomes too dry, and air can enter the tensiometer tube, making it ineffective.
(a) 0.8 bars: Correct. Tensiometers accurately measure soil water tension up to 0.8 bars.
(b) 1.2 bars: Too dry for tensiometer accuracy; air entry issues occur.
(c) 1.5 bars: Approaches the permanent wilting point; tensiometers are ineffective here.
(d) 1.8 bars: Well beyond the operating range of a tensiometer.