The basic unit of mass in the metric system is

That would be kinetic energy

The answer is 4f======since electrostatic force is given by    we let f be the electrostatic force when  r = 1 m    if we let  denote the electrostatic force when the distance is decreased so that r = 0.5m, then    we established earlier that f = kq₁q₂. therefore    the force will now be 4f.

Lexy is correct because angle r is between the incident wave,  n  = 0, and a diffracted wave.