<span>Thallium. 81 Protons, post-transitional metal that is not found in nature. </span>
I think that number five is lithium
Explanation:
Period of a mass on a spring is:
T = 2π√(m/k)
T is inversely proportional with the square root of k. So as the spring constant increases, the period decreases.
Mass is how heavy is it, weight is the size both are the same
