Question

an open u tube contains mercury when 13.6 cm of water is poured into one of the arms

Answer 1

Density of water is 1gm per cc

Density of mercury is 13.6 per cc.

So, clearly, adding 13.6 'cm' of water is just equivalent to adding a 'cm' of mercury, which will increase the mercury level in the other arm by 0.5 cm.

Thus the increase should be 0.5cm