50 g magnesium reacts with 100 ml of 0.02 M nitric acid (HNO3). How many liters of H2 will be produced?

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.

Iknow #2 is d. i just need to know why

There are main groups in the modern periodic table of elements