Assertion: A metallic shield in the form of a hollow shell may be built to block an electric field.
Reason: In a hollow spherical shield, the electric field inside it is zero at every point.
(A) If both assertion and reason are true but the reason is the correct explanation of assertion.
(B) If both assertion and reason are true but the reason is not the correct explanation of assertion.
(C) If the assertion is true but reason is false.
(D) If both the assertion and reason are false.
(E) If reason is true but assertion is false.

Hint: An assertion means the forceful or the confident statement or it may be fact and belief whereas the reason is an explanation about that particular statement. First we will find if the given assertion is true or false and then will decide whether the given assertion and the reason are correct or not.

Complete step by step answer:
In any metallic shield, due to the electric field the electric charge will be induced in such a way that the combination of the negative charge and the positive charge gives the net electric charge equal to zero. As a result at any point the electric field is zero. Hence, the metallic field in the form of the hollow shell probably is built to block an electric field.
Therefore, both the Assertion and the Reason are true and reason is the correct explanation of assertion.

Hence, from the given multiple choices- the option A is the correct answer.

Note: Always judge each given statement of the assertion and the reason independently. If you are able to find out the incorrect statement, then you have solved the statement and accordingly determine whether the given statements are true or false. These types of questions are generally asked in the competitive exams.