Cual es la concentracion % de una rebanada de pan de 28g con 3.4 ppm de sodio

0.00034% is the (w/w) concentration of sodium in 28 grams of bread.

Explanation:

Mass of bread = 28 g =0.028 kg (1 g = 0.001 kg)

The ppm concentration of sodium = 3.4

1 ppm = 1 mg/kg

The ppm concentration of sodium = 3.4 mg/kg

This means 3.4 mg of sodium is present in 1 kg of bread.

The mass of sodium present in 0.028 kilograms of bread will be:

Mass of sodium present in bread = 0.0952 mg

Mass of bread in milligrams = 28 g = 28000 mg

w/w % : The percentage mass is the mass of the of solute present in total mass of the solution.

0.00034% is the (w/w) concentration of sodium in 28 grams of bread.

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.

it means there are 3 atoms of oxygen