Why can't silver have a mass number of 107.87?

No because it not possibly

Idon't mean to be a smart alec, length of atoms' bonds is the simplest way to define it.

Answercan utilize even low wind speed to produce electricity;

The main types of electromagnetic radiation. radio  waves have  the lowest frequencies  and  longest  wavelengths, while gamma  waves have highest frequencies  and shortest wavelengths. the wavelengths vary across the electromagnetic spectrum from about 10–15 m to more than 104 m.hope it !