How many significant figures does 507.2m have?

4

Explanation:

To find the significant digits we have few methods.

METHOD 1--Count from left to right

A number that has a decimal point, count digits from the first number from the left that isn't zero.

METHOD 2--Count from right to left

A number that doesn't have a decimal point, count digits from the first number from the right that isn't zero.

It is obvious that 507.2 has a decimal point, so we count from left which we will start with 5.

5, 0, 7, 2

There are 4 digits.

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Explanation:

The spectra of the Sun and stars exhibited bright and dark lines called Fraunhofer lines. These were shown to be caused by elements emitting or absorbing light at specific wavelengths. Because each element emits or absorbs light only at specific wavelengths, the chemical composition of stars can be determined.