<u>Answer: </u>The correct statement is X is the effective nuclear charge, and it increases across a period.
<u>Explanation:</u>
We are given that:
X = number of protons − number of core electrons
Effective nuclear charge is defined as the actual nuclear charge (Z = number of protons) minus the screening effect caused by the electrons present between nucleus and valence electrons. These electrons are the core electrons.
The formula used for the calculation of effective nuclear charge given by Slater is:

where,
= effective nuclear charge
Z = atomic number or actual nuclear charge or number of protons
= Screening constant
The effective nuclear charge increases as we go from left to right in a period because nuclear charge increases with no effective increase in screening constant.
Hence, the correct answer is X is the effective nuclear charge, and it increases across a period.
The correct answer is 2.53 g of precipitate, BaCrO4.
Which is a correct description of the organization of subatomic particles in atoms?
Protons and neutrons are tightly packed into a small nucleus. Electrons occupy the space
outside the nucleus
hope this helps.
The process of an atom releasing energy when it moves to a lower energy state is called emission.