Answer:
Density is nearly 3 cabs per hectare
Explanation:
Given -
There are three three intertidal regions.
Area of each intertidal region is
hectares.
Number of crab in the intertidal regions are as follows -
Intertidal region I - 7
Intertidal region I - 2
Intertidal region I - 6
Sum of crabs in all three regions is equal to

Total area of all three intertidal regions is equal to
hectares
Now density per hectare is equal to total population of crab divided by total area of all the three intertidal regions
Density 
Density is nearly 3 cabs per hectare
Subtract the atomic number from the atomic mass to get the neutrons
<span>Among all choices, mobility is not a characteristic of a plant. Plants are multicellular organisms. They have organelles inside their cells and thus they are eukaryotes. Chloroplasts are organelles that are found in plant cells and they have an important role in the process of photosynthesis. However, plants cannot move from place from place like animals.</span>