Final answer:
The unknown charge has a magnitude of approximately 1.36 x 10^-6 C and, since the force is repulsive, it has a positive polarity.
Step-by-step explanation:
To find the magnitude and polarity of the unknown charge exerting a repulsive force, we use Coulomb's law which states that the force (F) between two charges (q1 and q2) is proportional to the product of their magnitudes and inversely proportional to the square of the distance (r) between them. Thus, the formula is F = k * |q1 * q2| / r^2, where k is Coulomb's constant (8.9875 x 10^9 Nm^2/C^2). Given that q1 is -2.3*10^-6 C (negative charge), F is 0.35 N, and r is 0.20 m, we can rearrange the formula to solve for q2: q2 = Fr^2 / (k|q1|). Substituting the given values, we calculate q2, which will be positive since the force is repulsive, indicating opposite charges. Using the calculation q2 = (0.35 N * (0.20 m)^2) / (8.9875 x 10^9 Nm^2/C^2 * 2.3 x 10^-6 C), we obtain q2 = approximately 1.36 x 10^-6 C. Therefore, the unknown charge has a magnitude of 1.36 x 10^-6 C and is positive.