Final answer:
Option a, which is 6 x 10¹¹, is the only number written in proper scientific notation because it is written as a product of a number between 1 and 10 (which is 6) and a power of 10.
Step-by-step explanation:
The question asks to identify which number is written in scientific notation. Scientific notation requires a number to be written as a product of a number between 1 and 10 and a power of 10. Looking at the options provided:
- a. 6 x 10¹¹ - This is already in the correct form, where the number 6 is between 1 and 10, and it's multiplied by 10 raised to a power, in this case, 11.
- b. 12 x 10⁻⁸ - This is not in correct scientific notation because the first number is not between 1 and 10. It would need to be rewritten as 1.2 x 10⁻⁷.
- c. 0.2 x 10⁵ - Similarly, this is also not correct scientific notation, as 0.2 is not between 1 and 10. It should be 2 x 10⁴ to be in proper scientific notation.
- d. 8 x 7² - This is not in scientific notation at all because it does not involve a power of 10.
Therefore, the number written in proper scientific notation is a. 6 x 10¹¹.