What determines the reactivity of an element?

Mass and velocity are the 2 factors used to calculate kinetic energy. the equation for kinetic energy is (1/2)mv^2. hope this !

Sounds propagates through some kind of medium. usually it's air, but it goes just as well through solid objects like walls, windows etc. a soundwave will compress the (air)molecules in front of it, and if this increased density wave hits your ears, you register it as sound. solid objects like walls are a lot denser than air, this means that they will damp a wave, but also carry it easier.

Idon't  know if i got it wrong but i picked ( a )