8.1) Here, Pressure increases with depth in the ocean at higher rate then that of increase in altitude in atmosphere. So, the rate of change of pressure is different in these journeys.So, your most correct answer would be option D.
8.2) Difference in the shape of lines is due to different density of air & water. So, that physical property and your answer would be option A
So, in Short Answers of your questions are:
8.1) - Option D
8.2) - Option A
Hope this helps!
Answer: 
Explanation:
Given
Radioactive material is found to decrease 40% of its original value in 
Sample at any time is given by

where, 
Put values

Taking natural logarithm both side

Answer:
860.6 years.
Explanation:
The parameters given are;
Initial detector activity = 370000 alpha decays per second
Final detector activity = 93000 alpha decays per second
Formula for time to change in activity is given by the following relation;

t₉₃₀₀₀ = 2.72 × 10¹⁰ seconds = 860.6 years.