Which number is not in scientific notation? 11 ⋅ 1021 5.7 ⋅ 109 3.1 ⋅ 10−12 1.67 ⋅ 10−5

11 * 10^21 is not in scientific notation.

Scientific notation requires that the digits part is greater than zero and less than 10 (it cannot be 10).

So, to put that number in scientific notation 11 must be converted to 1.1*10 and 11 * 10^21 is 1.1 * 10 * 10^21 = 1.1 * 10^22.

Note tha 11 * 10^21 is the same that 1.1 * 10^22 but the last is in scientific notation while the former is not.

All the other numbers have the digit part in the range [1,10), so they are in scientific notation.