Answer:(c)
Explanation:
Given : In a hypothesis testing the null hypothesis has been rejected when the alternative hypothesis has been true.
Find : to find that the given decision is create type I error , type II error or right decision has been taken
Step by step :
In hypothesis testing there are 2 types of error.
(1)Type I error :- if the null hypothesis is rejected when it is true, is known has Type I error .
(2)Type II error:- if the null hypothesis is accepted when alternative hypothesis is true, is known as type II error.
Since here null hypothesis has been rejected when alternative hypothesis has been true,i.e., the correct decision has been made
Hence option (c) is correct.