Final answer:
The number 1.09 x 10¹ in decimal form is 10.9, achieved by moving the decimal point one place to the right due to the exponent of 1 on the 10.
Step-by-step explanation:
The number 1.09 x 10¹ expressed in decimal form is 10.9. In scientific notation, the exponent on the 10 indicates how many places to move the decimal point. Since the exponent is 1 (10¹), it means we move the decimal point one place to the right, giving us 10.9 as the answer. Therefore, the correct answer from the options provided is 4) 10.9.