What does relative humidity indicate?
a. how close air is to saturation
b. the amount of heating needed for evaporation
c. the amount of water vapor in the air
d. the ratio of water vapor to carbon dioxide in air

Ans A. how close air is to saturation

In general, humidity indicates the moisture content or the amount of water vapor in the air.

Relative humidity (RH) is the ratio of the amount of water vapor in the air to the amount of water vapor that the air can hold at that temperature.

RH = [Actual vapor density/Saturation Vapor density] *100

Relative humidity is temperature dependent. Higher the temperature, lower will be the value because high temperature will heat up the air causing it to expand. This will improve its ability to hold moisture thereby increasing the saturation vapor density and lowering the relative humidity.

Therefore, relative humidity indicates how close air is to saturation.

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.