You have a glass of pure water and add acidic lemon juice to it. this means that you are adding to it, and the solution will become

acid; acidic

Explanation:

You have a glass of pure water and add acidic lemon juice to it. This means that you are adding ACID to it, and the solution will become ACIDIC.

Pure water has a pH value of 7

Lemon juice has a pH value less than 7 i.e acidic

Therefore, addition of lemon juice to pure water will drop the latter pH from 7 to form a final solution that is ACIDIC.

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.

that tool would be a compass