Final answer:
The combined mass of Earth and Venus is calculated by adding their masses together to get 10.8 x 10^24 kg, which is then converted into proper scientific notation as 1.08 x 10^25 kg. Therefore, the correct option is B. 1.08 x 10^25 kg.
Step-by-step explanation:
To calculate the combined mass of Earth and Venus in scientific notation, you simply add the two masses together:
Earth's mass = 5.9 x 1024 kg
Venus's mass = 4.9 x 1024 kg
Combined mass = (5.9 + 4.9) x 1024 kg
Combined mass = 10.8 x 1024 kg
However, we must express 10.8 x 1024 kg in proper scientific notation, with only one non-zero digit to the left of the decimal point. Hence, 10.8 x 1024 becomes:
Combined mass = 1.08 x 1025 kg
Therefore, the correct answer is B. 1.08 x 1025 kg.