Question 342348
The hundred-thousandths place is the 5th place to the right of the decimal point.

Rounded as requested 0.000216453 becomes 0.00022.

We now write 0.00022 in scientific notation.  

The value in scientific notation must be between 1 and 10.

Moving 4 places to the right of the decimal, we get 2.2.

When we move to the right in scientific notation, the exponent value is negative and vice-versa.

So, the answer is 2.2 x 10^(-4).