How many significant figures are in the measurement 5 9 x 10^4 milligrams?

The measurement 5.9 x 10⁴ milligrams has two significant figures.

Here’s the explanation: The digits in a number are considered significant if they are non-zero, zeroes between non-zero digits, or trailing zeroes in a decimal number. In this case, the measurement 5.9 consists of the digits 5 and 9, both of which are non-zero and significant. The factor of 10⁴ does not affect the count of significant figures; it merely indicates the scale of the number.

Therefore, when counting significant figures, only the digits 5 and 9 are considered, resulting in a total of two significant figures for the measurement 5.9 x 10⁴ milligrams.