What combines to form compounds? a.) molecules b.) atoms of element c.) minerals d.) valences

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.

What 3 categories are elements divided

One student said that the investigation was not valid (a fair test). write a plan for the investigation that includes improvements to the method and apparatus