Atoms of elements at the top of a group on the periodic table are smaller than the atoms of elements at the bottom of the group. how does this explain the difference in the reactivity of metals within a group?

The metric unit of electrical power is the watt volt ampere ohm

Two identical stars with mass m orbit around their center of mass. each orbit is circular and has radius r, so that the two stars are always on opposite sides of the circle. (a) find the gravitational force of one star on the other. (b) find the orbital speed of each star and the period of the orbit. (c) how much energy would be required to separate the two stars to infinity?

Estimate of the number of stars in our galaxy