Answer: Option (1) is the correct answer.
Explanation:
Compounds are the substances which contain two or more different elements.
Similarly, water is a compound as it is made up when two hydrogen atoms combine with one oxygen atom. Compounds can be broken down with the help of chemical reactions.
Hence, the statement water can be broken down by chemical means explains why water is classified as a compound.
In reaction 1 of the Krebs cycle, acetyl‑CoA formed in the pyruvate dehydrogenase reaction condenses with the four‑carbon compound to form <em>citrate </em>with the elimination of coenzyme A. Since the product has three carboxyl groups, this pathway is referred to as the cycle. In reaction 2 of the Krebs cycle, this product then undergoes to form<em> isocitrate. </em>The enzyme is called aconitase because the compound cis‑aconitate is the <em>intermediate product</em> of the reaction. Reaction 3 eliminates CO2 to form the five‑carbon dicarboxylic acid <em>α-cetoglutarate. </em>Oxidation also occurs, with electrons transferred from the substrate to <em>COO-</em> . Consequently, this reaction is an oxidative decarboxylation.
In the image, you can see the reaction 2 in Krebs cycle is a two steps reaction with an intermediate cis-aconitase and a product called isocitrate.
The branch of chemist is a substance of science and pysical is the land science such as a desert of a forest those are chemist and physical science have a good day :)