How many moles of a gas would occupy 11.4 L at 273K and 2.00 atm?

As changes in energy levels of electrons increase, the frequencies of atomic line spectra they emit

The characteristics of two different types of reactions are shown below: reaction a: electrons are gained by the atoms of an element. reaction b: protons are lost by the atom of an element. which statement is true about the atoms of the elements that participate in the two reactions? their identity changes in both reaction a and reaction b. their identity changes in reaction a but not in reaction b. their identity changes in reaction b but not in reaction a. their identity remains the same in both reaction a and reaction b.

What is a number added in front of a formula in order to balance the equation