To determine the most appropriate answer, we need to analyze both the assertion and the reason given.
Assertion (A): In a particular point defect, an ionic solid is electrically neutral, even if few of its cations are missing from its unit cells.
Explanation of (A): If cations are missing, such a point defect is known as a Schottky defect. In a Schottky defect, equal numbers of cations and anions are missing, preserving the overall electrical neutrality of the ionic solid. Therefore, the assertion is correct because the absence of some cations does not disturb the electrical neutrality as enough number of anions are also absent.
Reason (R): In an ionic solid, Frenkel defect arises due to dislocation of cation from its lattice site to interstitial site, maintaining overall electrical neutrality.
Explanation of (R): A Frenkel defect involves a cation moving from its regular lattice position to an interstitial site, leading to a dislocation and not a loss of cations from the crystal structure. Thus, electrical neutrality is maintained in Frenkel defects as no ions are actually lost from the crystal. Therefore, the reason is also correct.
However, the given reason does not directly explain the assertion correctly. The assertion mentions the absence of cations which correlates with Schottky defect, not Frenkel defect.
Thus, the proper conclusion is:
Both (A) and (R) are correct and (R) is not the correct explanation of (A)
A sphere of radius R is cut from a larger solid sphere of radius 2R as shown in the figure. The ratio of the moment of inertia of the smaller sphere to that of the rest part of the sphere about the Y-axis is : 
A constant voltage of 50 V is maintained between the points A and B of the circuit shown in the figure. The current through the branch CD of the circuit is :
The current passing through the battery in the given circuit, is: 
Given below are two statements:
Statement I: The primary source of energy in an ecosystem is solar energy.
Statement II: The rate of production of organic matter during photosynthesis in an ecosystem is called net primary productivity (NPP).
In light of the above statements, choose the most appropriate answer from the options given below:
The matter is made up of very tiny particles and these particles are so small that we cannot see them with naked eyes.
The three states of matter are as follows: