What is the molar mass of a substance, if 0.4 mole of the substance has a mass of 25.0g?

The element with the electron configuration 1S\(^2\)2S\(^2\)2P\(^3\) is 

A decrease in atomic size and an increase in nuclear charge across a period lead to 

The order in which a mixture of sand, ammonium chloride and sodium chloride can be separated is

The idea of planetary electron was that of