Final answer:
To express 276 x 10⁷ in proper scientific notation, we need to move the decimal point 7 places to the left, resulting in 2.76 x 10⁹ (option c).
Step-by-step explanation:
To express the number 276 x 10⁷ in proper scientific notation, we need to move the decimal point until there is only one non-zero digit to the left of it. In this case, we need to move the decimal point 7 places to the left. This gives us the number 2.76. Since we moved the decimal point 7 places to the left, we write 10⁷ as the exponent. Therefore, the number 276 x 10⁷ expressed in proper scientific notation is 2.76 x 10⁹ (option c).