If 2 grams of substance A react completely with 3 grams of substance B, what must be true about the products?

To analyze the reaction given:

**Reactants:**
- 2 grams of substance A
- 3 grams of substance B

**Reaction:**
- 2 A + 1 B → 3 C + 1 D

**Products:**
- 3 moles of C
- 1 mole of D

Now, let's evaluate the options one by one:

**A. 1 gram of substance B is left over**
- This statement can't be true because it is mentioned that substance A reacts completely with substance B. Since 2 grams of A reacts with 3 grams of B, the reaction consumes all of both reactants.

**B. 2 moles of substance A are used**
- The reaction indicates that 2 moles of substance A are required, but the statement doesn't provide enough context about the molar mass of item A to confirm. Without that information, this statement can't be concluded definitively.

**C. 4 grams of products are produced**
- The total mass before the reaction is 2 grams (A) + 3 grams (B) = 5 grams. According to the law of conservation of mass, the total mass of the reactants will equal the total mass of the products. Therefore, 4 grams of products cannot be true, since that would not account for the total mass.

**D. 4 moles of products are produced**
- The products consist of 3 moles of C and 1 mole of D, which totals 4 moles (3 + 1 = 4). This statement is true.

**E. 5 grams of products are produced**
- Considering conservation of mass, since 2 grams of A and 3 grams of B react together, the total mass of products must also be 5 grams. This statement is also true.

Given these evaluations, the correct answers are:

**D. 4 moles of products are produced** and **E. 5 grams of products are produced.**