In which of the following scenarios would resistance increase?

Resistance increases when a conductor is stretched because stretching a material increases its length while reducing its cross-sectional area. According to the resistivity formula, resistance is directly proportional to the length of the conductor and inversely proportional to its cross-sectional area. Thus, when a conductor is stretched, the increase in length will lead to a higher resistance, while the reduced area contributes further to this increase.

In the context of the other scenarios, cooling a conductor typically leads to a decrease in resistance, as lower temperatures allow charge carriers to move more freely. A decrease in voltage across a conductor does not necessarily alter its resistance; instead, it affects the current flowing through it according to Ohm's Law. Lastly, if the temperature of a conductor remains constant, its resistance remains constant as well, provided that other factors, such as material properties and dimensions, do not change.