A point positive charge is brought near an isolated conducting sphere (figure). The electric field is best given by:

1.                        2.

3.                   4. 

Hint: The electric field lines will be perpendicular to the surface of the sphere.

Step 1: When a positive point charge is brought near an isolated conducting sphere without touching the sphere, then the free electrons in the sphere are attracted towards the positive charge. This leaves an excess of positive charge on the rear (right surface of the sphere).

Both kinds of charges are bound in the metal sphere and cannot escape. They, therefore, reside on the surface.

Thus, the left surface of the sphere has an excess negative charge and the right sphere has an excess positive charge as given in the figure below.

Step 2: An electric field line starts from a positive charge and ends at a negative charge (in this case from point positive charge to the negative charge created inside the sphere).

Also, electric field lines emerge from a positive charge, in the case of a single charge and end at infinity.

Here, all these conditions are fulfilled in Fig. (1).