Correct Answer  Option 2 : c
Concept:
Photon:
 A photon is a particle of light defined as a discrete bundle of electromagnetic energy.
 The rest mass of the photon is zero.
 Photons are stable particles.
 They do not have any electric charge.
 Photons are not affected by the magnetic field and electric field.
Postulates of Special Relativity:

The relativity postulate: the laws of physics apply in every inertial reference frame.
The speed of light postulate: The speed of light in a vacuum is the same for any inertial reference frame (c = 3 x 10^{8} m/s).
 This is true no matter how fast a light source is moving relative to an observer.
 This is due to either light is an exception, or the classical velocity addition formula only works at low velocities.
Relativistic Velocity Addition:
If two photons moving with speed u and v relative to each other, then, relative velocity will be
\(V_R = \frac{u  v}{1\frac{u\times v}{c^2}} \)
Calculation:
Given, photons are moving with speed c towards each other, therefore
u = c and v =  c
Using the relation of relative velocity
\(V_R = \frac{u  v}{1\frac{u\times v}{c^2}} \)
\(⇒ V_R = \frac{c + c}{1+\frac{c\times c}{c^2}} \)
⇒ V_{R} = c
Hence, the relative velocity of photons will be c.