Final answer:
Quantitative evidence in a lab includes measurements such as the weight of a substance before and after a reaction. This provides numerical data crucial for analysis, unlike qualitative descriptions of properties or personal opinions.
Step-by-step explanation:
An example of quantitative evidence you might collect in a lab is B. The weight of a substance before and after a reaction. This is because quantitative observations are measurements that consist of both a number and a unit, such as when using a balance (scale) to measure the mass (weight) of substances. These types of measurements provide actual numerical data that can be analyzed. For instance, determining if a reaction leads to a gain or loss in mass or confirming if mass is conserved during a reaction would involve quantitatively measuring the substances involved.
On the other hand, observations like color changes during a chemical reaction or descriptions of smells are considered qualitative evidence because they describe properties without numerical information. Personal opinions about the effectiveness of a procedure also do not provide objective, measurable data, and thus, are not quantitative.