Kindly explain question numbers 26 and 27

26).

The complete pattern of a pendulum is ...

-- out to one side

-- back to the center

-- out to the OTHER side

-- back to the center.

So, on the graph, the complete period is one up-loop and one down-loop.

That's 6 seconds. (b)

27).

This question is just asking for the frequency, without using the word.

Frequency is always (1/period).  That's 1/6 of a second. (a)

(This kinda makes sense.  If you want to do something in 6 seconds, you need to do 1/6 of it every second. Right ?)

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.