Question

multiple-choice question
how many significant figures are in the number 49.0 grams?
2
1
3
4

Explanation:

Step1: Recall significant figure rules

Significant figures: Non - zero digits are significant. Zeros between non - zero digits are significant. Trailing zeros in a decimal number are significant.
For the number 49.0: The non - zero digits 4 and 9 are significant. The trailing zero after the decimal is also significant.

Step2: Count the significant figures

We have 4, 9, and 0 (the trailing zero after the decimal). So we count 4, 9, and 0. That's 3? Wait, no. Wait, 49.0: 4 is significant, 9 is significant, and the 0 after the decimal is significant. Wait, 4, 9, 0. Wait, no, 49.0 has three significant figures? Wait, no, wait. Wait, 49.0: the digits are 4, 9, and 0. Wait, no, 49.0 is a decimal number. The rules for significant figures:

1. All non - zero numbers are significant. (4 and 9 are non - zero, so they are significant)
2. Zeros between non - zero numbers are significant. (There are no zeros between non - zero numbers here)
3. Trailing zeros in a number with a decimal point are significant. (The zero after the decimal is a trailing zero in a decimal number, so it is significant)

So we have 4, 9, and 0. Wait, that's three? Wait, no, 49.0: 4 (1), 9 (2), 0 (3). Wait, but wait, maybe I made a mistake. Wait, 49.0: the number is 49.0. So the significant figures are 4, 9, and 0. So that's 3? But wait, the options have 3 as an option? Wait, the options are 2, 1, 3, 4? Wait, the original question's options: let's check again. The options are 2, 1, 3, 4? Wait, the user's image shows options: 2, 1, 3, 4? Wait, no, in the image, the options are: first option 2, second 1, third 3, fourth 4? Wait, no, the user's image: "2", "1", "3", "4"? Wait, no, the number is 49.0. Let's re - apply the rules.

Rule 1: Non - zero digits are significant. So 4 and 9 are significant (2 digits so far).
Rule 3: Trailing zeros in a decimal number are significant. The zero after the decimal in 49.0 is a trailing zero in a decimal number, so it is significant. So now we have 4, 9, 0. That's 3 significant figures. Wait, but wait, 49.0: is the zero significant? Yes, because it's a trailing zero in a decimal. So the number of significant figures is 3? Wait, no, wait 49.0: 4 (1), 9 (2), 0 (3). So three significant figures. So the correct option is 3. Wait, but let's check again.

Wait, maybe I messed up. Let's take an example: 49 has 2 significant figures. 49.0 has 3 because the decimal and the trailing zero indicate that the zero is significant (it shows that the measurement was made to the tenths place). So 4 (1), 9 (2), 0 (3). So the number of significant figures is 3.

Answer:

3 (the option corresponding to 3, e.g., if the option is labeled as "3" then the answer is the option with 3)