Is 6.0 × 10 to the negative 4th power is a significant figure?​

Yes

Explanation:

First remember that a significant figure are basically values that contribute to the precision of a value. In any scientific notation the values are significant figures because these values stay the same. In this case we have two significant figures which is 6 and 0, you can further prove that they are significant figures by converting the notation into standard form.

Negative so move the decimal point to the left:

6 and 0 are the significant figures in this standard notation because it's precise to it's actual value which is 6.0.

To sum up, the values you have on the left side of a notation are significant figures since they will not change no matter if it's standard or scientific notation meaning it's precise.

Hope this helps.

c. 4.54 x 10–12 j happens to be correct