<span> Greenhouse gases were not historically present in the atmosphere.</span>
Answer:- Frequency is
.
Solution:- frequency and wavelength are inversely proportional to each other and the equation used is:

where,
is frequency, c is speed of light and
is the wavelength.
Speed of light is
.
We need to convert the wavelength from nm to m.
(
)

= 
Now, let's plug in the values in the equation to calculate the frequency:

=
or 
since, 
So, the frequency of the green light photon is
.
Answer:
Contact force is a force that requires a contact between two bodies and is ubiquitous in nature
Explanation:
The force is distributed in two categories i.e
Contact Forces are the forces which is requires a contact between two bodies to occur.
The Types of contact forces are given below:
- Tension Force
- Normal Force
- Air Resistance Force
- Applied Force
- Spring Force
Some common daily examples of the contact force are
- Frictional force between the tyres of a moving vehicle and the road.
- Air flowing in opposite direction of a moving object.
- Pushing a table with hand and the friction between its base and floor.
- Stretching a rubber band with hands etc.
Also non-contact forces are Gravitational force, Electrical force and Magnetic force.
Stop littering and polluting
<span>Compounds are composed of different elements in a fixed proportions. For example, 1 atom of oxygen (O) combines with 2 atoms of hydrogen (H) to form one molecule of water (H2O) compound. Similarly other numbers of atoms would produce other chemical compounds. Even adding 1 more atom of oxygen would convert the water (H2O) into hydrogen peroxide(H2O2). Even if we were only to list the ones we know there are over 20 million known compounds.
In order to list all possible compounds such a table would rapidly become combinatoric nightmare of such size that it would not be practical to use even with a computer database and it would consist of over 100 billion possible compounds containing only H, C, O and N.
Creating a table to handle all possible elements would mean a table of many trillions of compounds.</span>