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The most abundant naturally occurring gas is Nitrogen (N2), which makes up about 78% of air. Oxygen (O2) is the second most abundant gas at about 21%. The inert gas Argon (Ar) is the third most abundant gas. Argon is the most abundant rare gas in the atmosphere. It is represented by the symbol Ar. The atomic number of Ar is 18.

The Group 7 elements are called the halogens. They are placed in the vertical column, second from the right, in the periodic table . Chlorine (17), bromine(35) and iodine(53) are the first three of the Group 7 elements.

- The enthalpy change associated with the removal of the first electron from an isolated gaseous atom. - Ionization enthalpy is the minimum amount of energy required to detach from an isolated gaseous atom the most loosely bound electron and turn it into a gaseous cation.

The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium.

Carbon dioxide, a colorless gas having a faint sharp odor and a sour taste. It is a greenhouse gas. Global warming occurs when carbon dioxide (CO2) and other air pollutants collect in the atmosphere and absorb sunlight and solar radiation that have bounced off the earth’s surface. Normally this radiation would escape into space, but these pollutants, which can last for years to centuries in the atmosphere, trap the heat and cause the planet to get hotter. These heat-trapping pollutants—specifically carbon dioxide, methane, nitrous oxide, water vapor, and synthetic fluorinated gases—are known as greenhouse gases, and their impact is called GREENHOUSE EFFECT

- The troposphere is the first and lowest layer of the atmosphere of the Earth. - Gases mix at this layer. - Weather occurs here - Region where plants and animals breathe and live - Tropospheric pollution is caused due to the presence of unwanted gaseous or solid components in the air.

Mass of Solution = Mass of Solute + Mass of Solvent → 20g + 180g : Mass of Solution = 200g Mass Percent = \(\frac{Mass of Solute}{Mass of Solution} * 100%\) Mass percent = \(\frac{20}{200} * 100%\) Mass percent = 10%

The ideal metals to use for the task of recovering copper from an aqueous solution of copper sulphate are metals that are stronger reducing agents than copper but not reactive enough to react with the water that the solution consists of. Zinc, Aluminium, Iron are relatively inexpensive and being unreactive on exposure to water.

Reduction, any of a class of chemical reactions in which the number of electrons associated with an atom or a group of atoms is increased.

Redox (reduction/oxidation) describes all chemical reactions in which atoms have an increase or decrease in oxidation number (oxidation state).

The hydrogen atom is the simplest of all atoms: it consists of a single proton and a single electron

An oxide is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula.

Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest halogen and is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour.

fluorine (F), most reactive chemical element and the lightest member of the halogen elements. As the most electronegative element, it is extremely reactive.

- Calcium trioxocarbonate (IV) occurs abundantly in earth's crust as limestone, chalk and marble - Eggshell is made almost entirely of calcium carbonate (CaCO3) crystals.