Answer:
C. Carbon dioxide
Explanation:
Carbon dioxide is one of the end-product of combustion reactions involving many fuels today.
With the rapid increase in urbanization and technological development, man demand for energy increased tremendously. The discovery of fossil fuels paved the way for the astronomical increase in the concentration of carbon dioxide in the atmosphere. The burning of fossil fuels like coal and oil invovles the process where the carbon atoms present in these fuels combine with oxygen in the air to make CO2. This has resulted in an increase in the concentration of atmospheric carbon dioxide (CO2).
The burning fossil fuels for electricity, industry, heat, and transportation are the major sources of the emossion of carbon dioxide.
Also, the cutting down of trees for paper production, building construction and for the establishment of settlements also increase the concentration of carbon dioxide in the atmosphere. Trees are help remove carbon dioxide from the atmosphere through the process of photosynthesis. However, when these trees are cut down, carbon dioxide accumulates in the atmosphere.
Answer:
The light emitted by a light bulb is a form of radiation that occurs when the filament heats up and its thermal emission gains enough energy to move into the visible spectrum.
Explanation:
Light bulbs contain a filament which is heated up electrically. When this filament is heated up,energy in the form of heat is imparted to the electrons in the filament.
This thermal excitation of electrons ultimately leads to emission of light in the viable spectrum. This light is now radiated through a light bulb.
The full chemical symbol for an element<span> shows its mass </span>number<span> at the top, and its atomic </span><span>number at the bottom</span>
Explanation:
Atomic number is defined as the number of an element which represents total number of protons.
When an atom is neutral then it means it contains same number of protons and electrons.
On the other hand, atomic mass is defined as the sum of total number of protons and neutrons present in an atom.
Protons of every element remains fixed because it shows the identity of each element but if we change the number of neutrons then also identity of the atom will remain fixed. This is because changing the number of neutrons will not show any change in number of protons.
For example, 
and 
are isotopes of hydrogen and they have same number of protons but different number of neutrons.
Thus, we can conclude that number of neutrons can vary without changing the identity of the element.
