How many significant digits are there in the measurement 50,600 mg a)4 b)5 c)6 d)7

Five. The measurement 50,600 mg has five significant digits.

I presume that you are using the comma as a decimal separator.

The rules for significant figures are
1.Nonzero digits are always significant.
2.Any zeros between two significant digits are significant.
3.Final or trailing zeros are significant only if they are to the right of a decimal point.

•According to Rule 1, the 5 and 6 are significant.
•According to Rule 2, the 0 between the 5 and 6 is significant
•According to Rule 3, the final two zeros are significant.

Thus, there are five significant digits in the measurement 50,600 mg.

Note: If the comma is a thousands separator, the number has only three significant digits.