A barometer kept in an elevator reads 76 cm when it is at rest. If the elevator goes up with increasing speed, the reading will be
(a) zero
(b) 76 cm
(c) < 76 cm
(d) > 76 cm

(c) < 76 cm

If the elevator goes up at an increasing speed, then the effective value of g increases.
We know:
$P=\mathrm{\rho }gh$
So, h will have a lesser value for the same value of P if g increases.