Question

if the air pressure is more outside what will be the level of mercury

Answer 1

The level of mercury on a standard day is 29.92 inches (760mm).

That means the weight of the Earth’s atmosphere above a point on the Earth’s surface is the same as the weight of almost 30 inches of mercury.

It is also measured as 14.7 pounds per square inch.

When more air piles up over a certain area ( a high pressure area, or “ridge”), the equivalent column of mercury would be higher, as would the measurement in pounds per square inch

Answer 2

If the air pressure is more, to match that pressure, the mercury column will rise.
This is because the pressure of liquid column depends on h, d and g. Density and acceleration due to gravity remains constant. So for increase of pressure, height of liquid column will increase.
Hope it helps.