Convert 1 mm of hg into pascal. take density of hg= 13.6×10^3kg/m^3. g = 9.8m/s×s

1mm of hg pressure is supposed to be the extra pressured exerted by a column of mercury 1 mm high. 

So the weight of the column of mercury =  density * height * Area * g
               Area is the cross sectional area of the tube holding mercury.

Pressure exerted by this column =  Weight / area
             = density * height *  g
             = 13.6 * 10³ kg /m³ * 1* 10^-3 m * 9.81 m/sec²        
             = 133.416 Pascal  or Newton/meter²

 Height = 1mm (of mercury) column in the barometer.

The best answer is (a) which is universal law is in effect at all times. it is constantly at play in everything we do and governs our lives. it is also important to note that universal law applies to not only everything on earth, but everything in the universe as well, which is another reason why it is in effect at all times.

Transfer of electrons. hope it !