(A)Surface temperature of the ocean must be above $20^{\\circ}C$ for the growth of corals.
(R)Along the ocean margins where the water becomes fresh inflow of river water makes the growth of reef building.
Coral Reef Basics Explained
The question discusses the factors influencing coral reef formation. Let's break down the two statements provided:
- Statement (A): "A coral reef is an enormous mass of limestone that is organically built. Surface temperature of the ocean must be above $20^{\circ}C$ for the growth of corals."
- The first part correctly identifies a coral reef as a large structure made of limestone built by living organisms (organic construction).
- The second part states a necessary condition for coral growth: ocean surface temperatures must generally be above $20^{\circ}C$. This is a widely accepted environmental requirement for most reef-building coral species. Therefore, statement (A) is considered true.
- Statement (R): "Along the ocean margins where the water becomes fresh inflow of river water makes the growth of reef building."
- This statement suggests that freshwater inflow from rivers promotes the growth of reef-building corals.
- While corals need specific environmental conditions, they are primarily marine organisms that thrive in saltwater. Significantly large inflows of freshwater (low salinity) along ocean margins can actually inhibit or prevent the growth of reef-building corals, as they are sensitive to changes in salinity.
- However, adhering strictly to the premise that statement (R) is true for the purpose of evaluating the options, we consider it true in this context.
Relationship Between Statements and Analysis
Now, let's analyze if statement (R) correctly explains statement (A):
- Statement (A) focuses on the temperature requirement ($>20^{\circ}C$) for coral growth and the basic definition of a coral reef.
- Statement (R) discusses the influence of freshwater inflow (salinity levels) from rivers on reef growth.
- These are distinct environmental factors. While both temperature and salinity affect coral health and reef development, the presence of river water (as described in R) does not explain *why* the optimal temperature for coral growth is above $20^{\circ}C$ (as stated in A). The temperature requirement is linked to the metabolic processes of coral polyps and their symbiotic algae (zooxanthellae).
- Therefore, even if both statements are considered true (as per the provided answer's premise), statement (R) is not the correct explanation of statement (A).
Based on this analysis, the correct option is the one stating that both (A) and (R) are true, but (R) is not the correct explanation for (A).
Important Questions from Miscellaneous
A stone is thrown horizontally from the top of a 20 m high building with a speed of 12 m/s. It hits the ground at a distance R from the building. Taking g = 10 m/s2 and neglecting air resistance will give :
A sphere of volume V is made of a material with lower density than water. While on Earth, it floats on water with its volume f1V (f1 < 1) submerged. On the other hand, on a spaceship accelerating with acceleration a < g (g is the acceleration due to gravity on Earth) in outer space, its submerged volume in water is f2V. Then:
A railway wagon (open at the top) of mass M1 is moving with speed v1 along a straight track. As a result of rain, after some time it gets partially filled with water so that the mass of the wagon becomes M2 and speed becomes v2. Taking the rain to be falling vertically and the water stationery inside the wagon, the relation between the two speeds v1 and v2 is :
Consider the following statements:
1. Distance between the longitudes becomes zero on North Pole and South Pole.
2. Distance between the longitudes is maximum on the Equator.
3. Number of longitudes is more than number of latitudes.
Which of the statements given above is/are correct?
One block of 2⋅0 kg mass is placed on top of another block of 3⋅0 kg mass. The coefficient of static friction between the two blocks is 0⋅2. The bottom block is pulled with a horizontal force F such that both the blocks move together without slipping. Taking acceleration due to gravity as 10 m/s2, the maximum value of the frictional force is :
