Hi I am Mary and I need help solving these questions

Read the given expression. x = number of protons − number of core electrons which of the following explains the identity of x and its trends across a period? x is the effective nuclear charge, and it remains constant across a period. x is the screening constant, and it remains constant across a period. x is the effective nuclear charge, and it increases across a period. x is the screening constant, and it increases across a period.

650.j is the same amount of energy as? 2720cal1550cal650.cal2.72cal

All forces cause motion? true or false