Answer:
D. Visible Light
Explanation:
D is the right answer because visible light is perceived by humans as color and the rest aren't visible at all. For example, if you broke a bone and have to have an X-ray done, you can't see the x-rays. When you are heating something in the microwave, you can't see the waves. And when you are listening to the radio in the car, you also can't see the waves.
Answer:
The number of moles =

The number of molecules =

Explanation:
Volume of the sphere is given by :

here, r = radius of the sphere


Radius = 3 mm
r = 3 mm
1 mm = 0.01 dm (1 millimeter = 0.001 decimeter)
3 mm = 3 x 0.01 dm = 0.03 dm
r = 0.03 dm
<em>("volume must be in dm^3 , this is the reason radius is changed into dm"</em>
<em>"this is done because 1 dm^3 = 1 liter and concentration is always measured in liters")</em>



(1 L = 1 dm3)
Now, concentration "C"=
The concentration is given by the formula :

This is also written as,

moles
One mole of the substance contain "Na"(= Avogadro number of molecules)
So, "n" mole of substance contain =( n x Na )

Molecules =

molecules
Magnesium is classified as a metal. Magnesium has two valence electrons