Final answer:
The formula of a binary compound from the provided list is a. P4O10, which is phosphorus pentoxide, a binary covalent compound consisting of two different elements - phosphorus and oxygen.
Step-by-step explanation:
The student's question relates to the identification of a binary compound from a given list. A binary compound is composed of two different elements. From the options provided (a. P4O10, b. CaCO3, c. NH4OH, d. Pb(NO3)2), the correct answer is a. P4O10, which is phosphorus pentoxide, a binary covalent compound formed by phosphorus and oxygen. Binary covalent compounds like P4O10 have their molecular formula showing how many atoms of each element are in a molecule, with the symbol of the element closer to metals usually written first. The other options (b, c, and d) are not binary compounds because they contain more than two different elements, as they include polyatomic ions or additional elements.