A point charge is

Option (c) is correct:

In an electric field, if a positive charge is placed, then the charge itself will generate some electric field on its own diverging from the point.

At a nearby point Q (towards the direction of external field), the field will increase as the field lines from the charge will also add to external field lines.

At a nearby point P (away from the direction of external field), the field will decrease as the field lines from the charge will cancel some of the external field lines.

Therefore, at a nearby point, field can either increase or decrease.

Option (d) is correct:

In an electric field, if a negative charge is placed, then the charge itself will generate some electric field on its own converging to the point.

At a nearby point Q (towards the direction of external field), the field will decrease as the field lines from the charge will cancel some of the external field lines.

At a nearby point P (away from the direction of external field), the field will increase as the field lines from the charge will add on to the external field lines.

Therefore, at a nearby point, field can either increase or decrease.