$0.000006723$ when expressed in scientific notation, is

### Concept & Logic When converting a small decimal number to scientific notation ($a \times 10^n$), shifting the decimal point to the right results in a negative exponent. ### Step-by-Step Solution **Given:** $0.000006723$ We need a coefficient $a$ such that $1 \le a < 10$. Place the decimal immediately after the first non-zero digit (6) to get $6.723$. Count the number of places the decimal point must move from its original position to its new position between the 6 and 7. Original: $0.000006723$ Move right: 1, 2, 3, 4, 5, 6 places. Since the decimal moved 6 places to the right to represent a number smaller than 1, the exponent is $-6$. Result: $6.723 \times 10^{-6}$ ### Exam Strategy & Shortcut Count the leading zeros, including the one before the decimal point. There are exactly 6 zeros ($0.00000$). For standard scientific notation of decimals, the negative exponent directly matches the total number of leading zeros. Hence, $10^{-6}$. ### Common Pitfall Counting only the zeros *after* the decimal point (which is 5) and incorrectly selecting an option with $10^{-5}$, or failing to convert the coefficient to a number strictly between 1 and 10. ### Final Answer Therefore, the correct answer is $6.723 \times 10^{-6}$.