Identify the exact number(s), if any, in each of the following pairs of numbers: a. 5 pizzas and 50.0 g of cheese

Exact numbers are values that are counted or defined and have no uncertainty associated with them. For example, if you have 5 pizzas, this number is exact because it represents a count of whole items. Exact numbers do not affect the precision of calculations in the same way that measured numbers do.

Measured numbers are values obtained from measurements and include some degree of uncertainty. For instance, 50.0 g of cheese is a measured number, as it is derived from a scale and reflects a specific quantity with a defined precision. The number of significant figures in a measured number indicates the level of certainty in the measurement.

Significant figures are the digits in a number that contribute to its precision. This includes all non-zero digits, any zeros between significant digits, and trailing zeros in the decimal portion. Understanding significant figures is crucial for accurately reporting measurements and performing calculations in chemistry, as they reflect the reliability of the data.