20 mL of standard hard water having 2200 mg/L of CaCO3 when titrated against EDTA solution which gave an end point at 19 mL. The same EDTA was used to titrate 29 mL sample hard water
which gave an end point at 25 mL. 100 mL of the same hard water sample was boiled, cooled
and filtered and made up with distilled water to 100 mL. 23 mL of this water sample consumed
15 mL of the same EDTA. Calculate the temporary, permanent and total hardness of the water
sample.

Explanation:

cube of any positive integer is of the form 9m,9m+1 or 9m+8. In this question, why do we take a=3q, a=3q+1 and a=3q+2. why cant we take a=2q and a=2q+1. or a=5q, 5q+1, 5q+2, 5q+3 and 5q+4. why do we specifically use a=3q and 3q+1 if a is any positive integer and can be represented in other ways?

Barometric pressure is just the same as atmospheric pressure. It is called barometric pressure because the instrument used to measure is called barometer. It is the pressure exerted by the air at a certain altitude. Since it is the pressure exerted by the air, it is also known as the weight of the air above the Earth. Depending on the altitude at which the measurement is done, barometric or atmospheric pressure varies, but the barometric pressure at sea level is 1 atm (atmosphere). It is equivalent to 101325 Pa (Pascal), 760 torr, 760 mm Hg and 1.01325 bar.