Question

which particles have the strongest attraction?

Explanation:

Step1: Recall Coulomb's law

The force of attraction between two charged particles is given by $F = k\frac{q_1q_2}{r^2}$, where $k$ is a constant, $q_1$ and $q_2$ are the charges of the particles, and $r$ is the distance between them. When the distance $r$ is the same, the force is directly proportional to the product of the charges $q_1q_2$.

Step2: Calculate charge - product for each case

For the top - left pair: $q_1 = 2$, $q_2=- 2$, and $q_1q_2=-4$. For the top - right pair: $q_1 = 1$, $q_2=-1$, and $q_1q_2=-1$. For the bottom - left pair: $q_1 = 1$, $q_2=-1$, and $q_1q_2=-1$. For the bottom - right pair: $q_1 = 2$, $q_2=-2$, and $q_1q_2=-4$. But the bottom - right pair has the smallest distance $r$ as the particles are in contact. Since $F$ is inversely proportional to $r^2$ and directly proportional to $q_1q_2$, the bottom - right pair has the strongest attraction.

Answer:

The pair with $2+$ and $2 -$ particles in contact.