Question

which of the following is a homonuclear diatomic molecule?
a) 2co₂
b) nh₃
c) co
d) h₂
question 2 (5 points)
mass and energy are conserved
a) in chemical changes and physical changes.
b) only in physical changes.
c) only in chemical changes.

Explanation:

• A homonuclear diatomic molecule consists of two atoms of the same element.
• For option A, \(2CO_2\) is a polyatomic molecule (carbon and oxygen atoms) and there are 2 molecules of \(CO_2\), not a diatomic molecule.
• For option B, \(NH_3\) is a polyatomic molecule (nitrogen and hydrogen atoms), not a diatomic molecule.
• For option C, \(CO\) is a diatomic molecule but it is heteronuclear (different elements: carbon and oxygen).
• For option D, \(H_2\) is a diatomic molecule (\(H - H\)) and it is homonuclear (both atoms are hydrogen).
• According to the law of conservation of mass and energy, mass and energy are conserved in both chemical and physical changes. In physical changes (e.g., melting of ice: \(H_2O(s)\to H_2O(l)\), mass of \(H_2O\) is conserved). In chemical changes (e.g., \(2H_2 + O_2\to 2H_2O\), mass of reactants \(= \) mass of products, and energy is also conserved as per the first law of thermodynamics (energy can be converted from one form to another but the total energy of an isolated system remains constant)).

Answer:

For the first question: D. \(H_2\)
For the second question: A. in chemical changes and physical changes.