A good vacuum produced in common lab apparatus corresponds to `10^(-6)` torr at `25^(@)C`. Calculate number of molecules per cubic centimeter at this T and P. In scientific notation, `x xx 10^(y)`. Find the value of `y`.

A beam of light has three lambda, 4144 "Å", 4972 "Å" "and"6216 "Å" with a total intensity of 3.6 xx10^(-3) Wm^(-2) equally distributed amongst the three lambda. The beam falls normally on an area 1.0 cm^(2) of a cleam metallic surface of work function 2.3 eV. Assume that there is no loss of light by reflection etc. Calculate the no. of photoelectrons emitted in 2 sec, in scientific notation, x xx 10^(y) find the value of y.

Average life time of a hydrogen atom excited to n=2 state is 10^(-8) s. Find the number of revolutions made by the electron on an average before it jumps to the ground state. If your answer in scientific notation is x xx 10^(y), then find the value of y.

Oxygen is present in a 1-litre flask at a pressure of 7.6 xx 10^(-10) mmHg at 0°C. Calculate the number of oxygen molecules in the flask.

Calculate the number of molecules persent in 1.12xx10^(-7) c.c. of a gas at STP (c.c.- cubic centimeters = cm^(3) ).

2.24 dm^(3) of dry ammonia gas contain 6 x 10^(22) molecules at S.T .P. Calculate the number of molecules in 56 cm^(3) of dry nitrogen at S.T.P.

Oxygen is present in a 1 litre flask at a pressure of 7.6 xx 10^(-10) mm of Hg. Calculate the number of oxygen molecules in the flask at 0^@C