B- lack of control.
the scientists did not have a proper control group.
The correct choice is Buffers.
Buffers contains both acids and bases in equilibrium.when base is added to buffers, they adjust the pH value by releasing hydrogen ions.when acid is added to buffers, they adjust the pH value by consuming hydrogen ions. hence these substances resist any change in their pH value by releasing or absorbing hydrogen ions.This process keeps the pH value constant.
Answer:
Explanation:
For simple pendulum the formula is
Where T is time period , l is length and g is acceleration due to gravity .
n is frequency
Putting the values
l = 1.584 m