Which of the following pure substances can be classified as an element?

• A. H_2
• B. H_2SO_4
• C. NO_3
• D. NaCl

Answer: (A)

Verified step by step guidance

1. Understand the definition of an element: an element is a pure substance consisting of only one type of atom. It cannot be broken down into simpler substances by chemical means.
2. Examine each given substance to determine its composition:
3. - \(H_2\): This is a molecule made of two hydrogen atoms, which are the same element, so it is a pure element.
4. - \(H_2SO_4\): This is sulfuric acid, a compound made of hydrogen, sulfur, and oxygen atoms, so it is not an element but a compound.
5. - \(NO_3\): This is the nitrate ion, composed of nitrogen and oxygen atoms, so it is a polyatomic ion and not an element.
6. - \(NaCl\): This is sodium chloride, a compound made of sodium and chlorine atoms, so it is not an element but a compound.