<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.
Answer:
i'm pretty sure it's 'transport oxygen from the lungs to tissues around the body'
Thomson's model included Protons and Electrons. His model is referred to as 'Plum Pudding' because of it.
A mineral is a naturally occurring, inorganic solid with a definite chemical composition and a crystalline structure formed by geological processes. A rock is an aggregate of one or more minerals whereas a rock may also include organic remains and mineraloids.