To evaluate 21/9 to 3 significant figures, we need to round the result to the nearest thousandth.
The result of 21 divided by 9 is 2.33333333333...
The third digit after the decimal point is 3, which is greater than or equal to 5. Therefore, we need to round up the second digit after the decimal point, which is 3.
Therefore, rounding 2.33333333333... to 3 significant figures gives us 2.33.
Therefore, the correct option is 2.33.