Question

Ortho and para hydrogen differ in:
(A) Atomic number
(B) Mass number
(C) Electron spin in two atoms
(D) Nuclear spin of two atoms

Answer 1

Hint: Molecular dihydrogen are generally of two types: ortho hydrogen and para hydrogen. This categorization is created based on an important property of their nuclei.

Complete step by step solution
A dihydrogen molecule (${H_2}$) can be divided into two types: ortho hydrogen and para hydrogen.
A dihydrogen molecule has two hydrogen atoms. The nuclei of both the atoms are proven to be spinning. Now, depending upon the direction of the spin of the two nuclei, the molecular hydrogen has been categorized into two types.
Ortho hydrogen: In the ortho hydrogen, the nuclei of both the two hydrogen atoms are spinning in the same direction.
Para hydrogen: In the para hydrogen, the nuclei of both the two hydrogen atoms are spinning in the opposite direction.
An ortho hydrogen is said to be more stable than the para hydrogen. This is because, in ortho hydrogen, the nuclei are having the same spin. On the other hand, in para hydrogen, both the nuclei are having an opposite spin. The spin in the same direction always favours the stability.
Generally, dihydrogen is a combination of ortho and para hydrogen that stay in the equilibrium.
$Ortho\left( {{H_2}} \right)\underset {eq.} \leftrightarrows Para\left( {{H_2}} \right)$
Now, let’s look at the answer options available:
* Both the ortho and para hydrogen have the same atomic number (1). Thus, they don’t differ in atomic number. Hence, option A cannot be true.
* Both of them have the same mass number (2). Thus, they also don’t differ in mass number. Hence, option B cannot be true.
* Dihydrogen is not divided based on the direction of spin of the electrons, rather they are divided based on the direction of spin of the two nuclei. Hence, option C cannot be true.

Hence option D is the correct answer to this question.

Note: Student’s sometimes get confused between the spin of the nucleus and spin of the electron. Nuclei spin around their own orbit, while electrons spin around the nucleus. Here, ortho and para hydrogen differ in nuclei spin direction not electron.