How many atoms are in 3.690 moles of oxygen

1 mole of any substance contains Avogadro's number.  

So, 1 mole of O2= 6.023x10^23 molecules  

3 mole of O2= 6.023x10^23x3 molecules  

= 1.8069x10^24 molecules  

Each molecule of Oxygen has 2 atoms.  

therefore,  

1.8069x10^24 molecules= 1.8069x10^24 x 2 atoms  

= 3.6138x10^24 atoms.

in scientific notation, the value of the  speed of light in a vacuum

  will be written as 2.995 * 10^8. when this value is represented in the form of

  a * 10^b, then, a = 2.995 and b = 8.

the value of the speed of light in a vacuum given above can also be rounded up to approximately 300000000. in this case, the scientific notation will be written as 3 *10^8.