Final answer:
A +20 nC charge should have 20 field lines, which is four times the number of electric field lines as a +5 nC charge. This is because the number of electric field lines is proportional to the charge's magnitude.
Step-by-step explanation:
d. 20 field lines. If five electric field lines represent a +5 nC charge, then a +20 nC charge, having four times the amount of charge, should logically have four times the number of electric field lines, resulting in 20 field lines.
The explanation for this is tied to the visual representation of electric fields. Electric-field lines provide a visual means to represent the strength and direction of an electric field surrounding a charged object. The number of lines drawn in diagrams is proportional to the magnitude of charge; more charged objects have more lines representing their electric field. In this scenario, the charge of +20 nC is exactly four times that of the +5 nC charge. Consequently, the number of electric field lines depicting the electric field generated by the +20 nC charge should also be four times greater, equating to a total of 20 electric field lines.