Is hydrogen a molecule and a compound?

What substance has a mass of 9.5g and volume of 2.1cm^3

Which statement is true about the model of the electromagnetic spectrum a: it change the frequencies of light. b: it compare wavelengths of light. c: the color of light waves can be changed using the model. d: the intensities of light waves can be decreased using the model.

How does electronegativity changes as we move from left to right across a period