Answer: the resource which they are not likely to compete for is CARBONDIOXIDE. The correct option is C.
Step-by-step explanation:
Competition may be defined as the a negative effect on plant growth which occurs when there is reduction in the availability of resources.
During the growth of plants, there are several resources that affects it's growth and maintenance. These resources include:
--> soil nutrients,
--> water,
--> carbondioxide and
--> sunlight
Since plants are autotrophs, that is, they manufacture their own food through the use of inorganic raw materials such as water and carbondioxide in the presence of sunlight, there may exist some level of competition for these resources when there is lack of space.
But plants are NOT likely to compete for carbondioxide because the atmospheric pool of carbondioxide is large and well mixed, therefore it won't be affected by lack of space between the two plants. Unlike the other main resources such as soil nutrients and water which are highly competed for and can determine the distribution of plants in an ecosystem.