In an experiment done in a physics laboratory class, ten students were tasked to record the period of a simple pendulum using identical time pieces. The following measurements were recorded: 2.1s, 2.1s, 2.2s, 2.4s, 2.3s, 2.2s, 2.4s, 2.2s, 2.5s and 2.3s. Solve the following and write a conclusion about them:

a. Mean b. Variance c. Standard deviation d. Measured period of the pendulum