Final answer:
Significant digits reflect the precision of a measurement. The given quantities contain four, five, two, and four significant figures, respectively. The determination of significant figures includes counting all non-zero numbers, zeroes between significant digits, and final zeros to the right of the decimal in a measurement.
Step-by-step explanation:
The number of significant digits (also known as significant figures) in a measured quantity reflects the precision of that measurement. Here's how to identify them in the given quantities:
- a. 1.008 g/mol: Contains four significant digits. All non-zero digits are significant, and zeros between other significant digits are also significant.
- b. 6.2402 km/hr: Contains five significant digits. Here, both the leading non-zero digits and the trailing non-zero digit after the decimal point are significant, including the zeros between them.
- c. 1800 yr: Contains two significant digits. Without a decimal point, trailing zeros are not considered significant.
- d. -124.0°C: Contains four significant digits. The minus sign is not counted as a digit; it indicates the temperature is below zero. The zero after the decimal point is significant because it denotes precision.
Remember, significant digits include all non-zero numbers, zeros between significant digits, and all final zeros that are to the right of the decimal point.