The question asks about the abundance of Dihydrogen (Hydrogen) in the universe by mass. This is a fundamental fact in cosmology and astrophysics. We need to recall the approximate cosmic abundances of the lightest elements.
Correct Option: C) More than 70%
The question asks about the primary form in which hydrogen is found on Earth. Hydrogen is the most abundant element in the universe, but on Earth, its occurrence is largely dictated by its chemical reactivity.
Correct Option: D) Combined form, such as in water and organic compounds
On Earth, hydrogen is almost exclusively found in chemical compounds due to its high reactivity. The most prominent examples are water (\(H_2O\)) and various organic compounds (e.g., methane \(\text{CH}_4\), glucose \(\text{C}_6\text{H}_{12}\text{O}_6\), proteins, etc.). Free dihydrogen gas (\(H_2\)) is very rare in Earth's atmosphere because it is light and reactive.
The question asks to identify the third naturally occurring isotope of hydrogen, given protium and deuterium. Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Hydrogen has three main isotopes, which are distinguished by their mass numbers.
D) Tritium is the third naturally occurring isotope of hydrogen, containing one proton and two neutrons. It is radioactive.
The question asks for the mass number of protium, which is the most common isotope of hydrogen. To answer this, we need to recall the definition of mass number and the composition of protium.
B) 1 — As determined from its composition of one proton and zero neutrons, the mass number of protium is 1.
The question asks to identify the common symbol for Deuterium, an isotope of hydrogen. To answer this, we need to recall the standard notation for isotopes, especially those of hydrogen.
C) D (or ²H) — This is the correct representation for Deuterium. \(\text{D}\) is the common special symbol, and \(^2\text{H}\) is its standard isotopic notation, indicating an atomic number of 1 (implied) and a mass number of 2.
This question tests knowledge of the common symbols used to represent isotopes of hydrogen, specifically tritium. Understanding the atomic structure of hydrogen isotopes is key to identifying their correct notation.
C) T (or ³H) is the correct symbol for tritium. Tritium is the isotope of hydrogen with one proton and two neutrons, giving it a mass number of 3. Hence, it is represented as ³H or by its special symbol T.