When a point charge of q is placed on one corner of a square, an electric field strength of 2 N/C is observed at the center of the square. Suppose three identical charges of q are placed on the remaining three corners of the square. What is the magnitude of the net electric field at the center of the square

Explanation:

Net electric field at the centre will be zero .

Since all the charges are equal and they all are symmetrically situated around the centre . So the electric field produced by each will cancel  out each other and hence the resultant electric field will be zero . It happens because electric field is a vector quantity and therefore it adds up vectorially . All the four electric field will form two pairs , in each pair electric fields are acting in opposite direction . So they all cancel out to zero .

the answer is b ) square root of 5