A good maximum sample size is usually around 10% of the population, as long as this does not exceed 1000. For example, in a population of 5000, 10% would be 500. In a population of 200,000, 10% would be 20,000.

Which method can be used for consequential questions?

Telephone Survey. Pros: This method can be used for asking consequential questions. It provides anonymity better than face-to-face interviews.

Which one the following test is applicable for N 30?

Further, t-test may be used in case of both small sample ( n<30) and large sample (n>30), but Z-test can be used in case of large samples only.