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

Based on the reaction equation you provided, \( 2A + IB \rightarrow 3C + ID \), we can analyze the situation with the given masses of the reactants (2 grams of substance A and 3 grams of substance B).

To evaluate the options concerning the products:

1. **1 gram of substance B is left over**: This can only be true if B is in excess during the reaction. However, without knowing the molar masses of A and B, we cannot determine if there is leftover B.

2. **2 moles of substance A are used**: This statement addresses the amount used concerning its molar mass. Since we only have mass and no molar mass provided, we cannot confirm this.

3. **4 grams of products are produced**: According to the law of conservation of mass, the total mass of the products must equal the total mass of the reactants. We started with a total of 2 grams of A + 3 grams of B = 5 grams of reactants. Therefore, the products must also total 5 grams. This option is **false**.

4. **4 moles of products are produced**: Similar to the previous analysis, we cannot verify the moles of products without knowing the molar masses, so this statement cannot be confirmed.

5. **5 grams of products are produced**: Since the mass of the reactants (5 grams) must equal the mass of the products, this statement is **true**.

So, based on the analysis, option **5 grams of products are produced** is the correct answer.