Answer:
100°C
Explanation:
The boiling point of water is 100°C and the difference is when will the water start boiling.
45,000 written in scientific notation would be 4.5×10⁴.
The number first has to be written so that there's only one number to the left of the decimal point.
4.5000
The decimal point would have to be moved 4 places to the right for the decimal to become 45,000 again. Therefore, the exponent on the 10 would be positive 4.
An accepted and universally true explanation of observed facts is a law.
Answer:
Choice number two. The value of "X" in this equation should be constant for all elements across a period.
Explanation:
Electrons are negative while protons are positive. Electrons are attracted to the proton but repel each other.
Consider an atom where electrons occupy more than one energy level. Consider the Bohr Model for that atom. Protons in the nucleus attract the electrons towards the center of the atom. However, at the same time, electrons in the inner shell will repel the valence electrons. That creates an outward force that pushes the valence electrons away from the atom.
The two forces mostly balance each other, but the attraction is slightly stronger. As a result, the overall force on the valence electrons is attractive. The effective nuclear charge gives the number of protons required to produce an attraction of that strength if there was no repulsion at all.
The value of effective nuclear charge is approximately the same as atomic number minus the number of inner-shell electrons. Apparently, the "X" in this question stands for the number of inner-shell electrons.
By the Aufbau Principle, all spots in the inner shell must be filled before more electrons can be added. Additionally, atoms in the same period have the same number of inner shells. As a result, the number of inner-shell electrons will be the same for all atoms in each period. Hence, the value of "X" should stay (approximately) the same across each period.
Answer:
It absorbs ultraviolet (UV) radiation from the sun.
Explanation:
Excess UV radiation damages DNA, causing malignant skin cancers.
The ozone in the upper atmosphere is beneficial because it absorbs much of this harmful radiation.
