Question

1. which of the following statements is true about elements and compounds? a. the atoms composing elements are all the same type, and the ones composing compounds are different. b. compounds are less complex in terms of structure than elements. c. chemical symbols can be used to represent both elements and compounds. d. chemical formulas are only used for elements but not compounds. 2. chemical formulas - a. can have their coefficients changed without changing the number of atoms that compose them. b. only contain one chemical symbol since they are pure substances. c. can contain more than one chemical symbol since they represent compounds. d. can contain more than one reaction. 3. if a scientist wants to change the number of atoms in a compound without changing the identity of the substance itself, they should a. change the coefficient at the front of the molecule. b. change the subscript of one of the elements. c. be sure to change the identity of the atoms in the compound. d. build the molecular model without indicating the subscripts.

Explanation:

1. Elements are pure substances made of one - type of atom. Compounds are made of different elements chemically combined. So, A is incorrect as compounds have different types of atoms. B is incorrect as compounds can be more complex in structure than elements. C is incorrect as chemical symbols are used for both elements and compounds. D is correct as elements are different from compounds.
2. Chemical symbols represent elements. A pure substance can be an element or a compound. Elements have one chemical symbol, and compounds have multiple chemical symbols representing the different elements in them. So, A is correct as substances can have coefficients changed without changing the number of atoms that compose them in a chemical reaction context. B is incorrect as elements can be represented by single - chemical symbols. C and D are incorrect as they misstate the nature of chemical symbols in relation to compounds and elements.
3. Changing the coefficient in front of a molecule changes the number of molecules but not the identity of the atoms in the compound. Changing the subscript changes the identity of the compound. So, A is correct as changing the coefficient at the front of the molecule only changes the number of molecules and not the identity of the atoms in the compound. B is incorrect as changing the subscript changes the identity of the compound. C is incorrect as one cannot be sure to change the identity of atoms just by changing subscripts in a non - specific way. D is incorrect as building a molecular model without indicating subscripts doesn't address the question of changing the identity of atoms.

Answer:

1. D.
2. A.
3. A.