With no difference in temperatures and 100% humidity, will it rain? why or why not?

A humidity measurement of 100% does not actually mean that will rain. It means that air can hold specific content of moisture at given temperature in the form of vapor.

Water vapor is in form of invisible gas in the atmosphere. The presence of water vapor in air is expressed in terms of relative humidity. The relative humidity is the ratio of partial pressure of water vapor to the vapor pressure at equilibrium of water at give temperature.  

As we know that water from falling rain evaporates into the air that increases the humidity. But that does not bring humidity to 100%. Hence, we can say that when air is saturated or it is 100% humidity, it requires more than saturated air to make rain. Humidity only enhances the chances of rain. It is the clouds that form at relative humidity of 100%. But as our air is impure due to presence of suspended particular matter, the formation of droplet is more favorable. When the size of the water droplet increases, the cloud cannot hold the water droplets and that’s when it falls from the cloud as rain.  

On the basis of the above explanation is:

With no difference in temperature and 100% humidity, it might not rain as air requires more than saturated air to make rain. The clouds form at 100% humidity.  

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added

i think the answer is composed of atoms