What element has a 2+ charge when it has 54 electrons ?

The correct answer is Barium (Ba)

Explanation:

A neutral atom - without charge- has the same number of protons and electrons. The atomic number - that is, the number of protons - is the identity of the element.

If an atom has 2+ charge, it has lost 2 electrons. Since it has 54 electrons, the atomic number of the element is: 54 + 2 = 56.

From the Periodic Table, the element with atomic number 56 is Barium (Ba).

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.

a 20-cm-long, cylindrical graphite (pure carbon) rod is inserted into an oxidizing atmosphere at 1145 k and 1.013 x 105 pa pressure. the oxidizing process is limited by the diffu- sion of oxygen counterflow to the carbon monoxide that is formed on the cylindrical surface.