The correct option is A 0.89 cm of Hg
Applying the Bernoulli's equation between given points,
p1+12ρv21=p2+12ρv22 ...(i)
p1=ρHggh=13600×1×(10)−2×10 N/m2
v1=35×10−2 m/s
v2=65×10−2 m/s
Since pipe is horizontal (constant elevation), hence the potential energy terms will cancel out from both sides.
From Eq.(i),
(13.6×103×10×10−2)+12×103×(0.35)2=p2+12×103×(0.65)2
⇒p2=1210 N/m2
Hence, corresponding reading of mercury column,
h=p2ρHgg
⇒h=121013.6×103×10
⇒h=8.89×10−3 m
∴h=0.89 cm of Hg