RESEARCH METHODOLOGY

Detailed explanation-1: -The normal distribution assumes that the population standard deviation is known. The t-distribution does not make this assumption. The t-distribution is defined by the degrees of freedom.

Detailed explanation-2: -For performing a t test, we don’t need to know the population standard deviation. The same is true for z test, providing we have a large sample size (>30). Thus the correct option, the condition that is not required is: (b) The population standard deviation a is known.

Detailed explanation-3: -Answer and Explanation: The t distribution is symmetrical, bell-shaped and its shape depends on the degrees of freedom. The mean of the t-distribution is 0. Hence, option (B) is correct.