The number 0.00243 has how many significant digits?
a. 3
b. 4
c. 5
d. 6

The number 0.00243 has 3 significant digits.

The correct answer is option B. 0.00243 has three significant digits. This is because for a decimal number which is less than 1, all the digits except the leading zero after the decimal point are considered to be insignificant. Thus, the two zeroes after the decimal point are insignificant.Therefore, the remaining three digits i.e. 243 are the significant digits.