what is 0.000345 expressed in scientific notation?\n3.45×10²\n3.45×10⁴\n3.45×10⁻²\n3.45×10⁻⁴

Explanation:

Step1: Recall scientific - notation form

Scientific notation is $a\times10^{n}$, where $1\leqslant|a|\lt10$ and $n$ is an integer.

Step2: Move the decimal point

For the number $0.000345$, move the decimal point 4 places to the right to get a number between 1 and 10. So $a = 3.45$.

Step3: Determine the exponent

Since we moved the decimal point 4 places to the right, $n=-4$. So $0.000345 = 3.45\times10^{-4}$.

Answer:

D. $3.45\times 10^{-4}$