Which of the following include exact numbers? a) the speed of light in a vacuum is a physical constant; to the nearest m/s, it is2.99792 ×108 m/s. b) the density of mercury at 25°c is 13.53 g/ml. c) there are 3600 s in 1h. d) in 2003, the united states had 50 states.

Explanation:

Exact numbers are those numbers which are known with 100% certainty  or accuracy . Numbers having decimal are generally not exact because they are a part of long drawn decimal number after rounding off  to certain places after decimal.

On the basis of this definition we can say as follows

speed of light is 2.99792 ×108 . Here the number quoted is not an exact number because it is a rounded off figure of speed of light to five digits  after decimal .

Similarly density of mercury too is rounded off to two digits after decimal

so it is also not a exact number.

There are 3600 s in 1 h . Here 3600 s is  an  exact number because one hour has been defined as 3600 s . It is not measured by any instrument.

In 2003, the United States had 50 states. Here 50 is an exact number .  

the moon affects the earth gravitation ally, causing certain motions of that body and also producing tides in its ocean and atmosphere. the tidal wave in our atmosphere is, however, far too minute to be an effective cause in any known meteorological phenomenon.

explanation: