Assertion (A) : No object can travel faster than 3 x 10⁸ m/s.

Reason (R) : Speed of light is the highest attainable speed in nature.

Both (A) and (R) are true and (R) explains (A).

The speed of light traveling through a vacuum is exactly 299,792,458 meters (983,571,056 feet) per second. That's about 186,282 miles per second — a universal constant known in equations as "c," or light speed. 

According to physicist Albert Einstein's theory of special relativity, on which much of modern physics is based, nothing in the universe can travel faster than light. The theory states that as matter approaches the speed of light, the matter's mass becomes infinite. That means the speed of light functions as a speed limit on the whole universe.