<span>atoms are made of particles that have a negative charge.</span>
The number we need in order to answer the question belongs in the space between the words "is" and "of". You left that blank blank, so there really isn't any question here to answer.
HOWEVER ... the refractive index of a medium can never be less than 1.0 , so we know for sure that <em>choice-a can't be</em> the correct answer.
<span>Nothing happens to the pitch of a cell phone ring when the amplitude
of a sound wave increases.
Pitch and amplitude are both characteristics of a wave, but they're not
connected, and they don't influence each other.</span>
This question involves the concepts of average speed, distance, and time.
The average speed of the family is "2.5 mi/hr".
<h3>AVERAGE SPEED</h3>
The average speed is defined as the ratio of the total distance covered with the total time taken to cover it.

where,
- s = distance covered = 2.5 miles
- t = total time taken = 1 hour
- v = average speed = ?
Therefore,

v = 2.5 mi/hr
Learn more about average speed here:
brainly.com/question/12322912