Positive and negative charged objects will affect which type of field?

The answer for you is D the last one

C and D are both possible.
But we have no idea which one is correct based on the given illustration, because you didn't give the illustration.

Please check the attached picture

Density.

It's a measure of mass per unit volume (density measures how much "stuff" there is in a particular space).

Explanation:

As the given rod is attached to rigid supports as a result, the deformation occurring due to the change in temperature will cause stress in the rod.

Let us assume that P is the compressive force in the rod due to change in temperature.

So,        

                          =

                          =

Now, we will calculate the actual change in temperature as follows.

             

This means that the actual change in temperature is more than required for yielding.

(a)   Formula to calculate yielding stress is as follows.

             

           

                        =

                        =

                        =

Hence, stress in the bar when temperature is raised to is .

(b)  Now, we will calculate the residual stress as follows.

           

           

                          = 15.837 ksi

Therefore, stress in the bar when the temperature has returned to is 15.837 ksi.