Because it is made up of sodium, a metal, and carbon, a nonmetal.
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<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.
Claim: Earth's atmospheric CO2 levels were measured over the past 1000 years and correlated with average world temperatures. The data demostrate that Earth's temperature did not change during the period CO2 levels were steady. But the past 100 years show a dramatic rise in CO2 levels, with a corresponding rise in world temperatures. The CO2 rise can be traced back to the start of the industrial revolution, when machines began doing much of the work. These machine burn fossil fuels and the increased CO2 levels have led to a dramatic rise in world temperatures. The data clearly show the importance of reducing fossil fuel useage, as well as other CO2 emitters. A world of incresing temperatures will lead to greater natural disasters, such as storms, flooding, hurricanes, and drought - all of which upset the ecological balance of the planet.
Your answer would have to be #3