Forming a covalent bond
A covalent bond is formed when two atoms share a pair of electrons. Covalent bonding occurs in most non-metal elements, and in compounds formed between non-metals.
These shared electrons are found in the outer shells of the atoms. Usually each atom contributes one electron to the shared pair of electrons.
The slideshow shows how a covalent bond forms between a hydrogen atom and a chlorine atom, making hydrogen chloride.
Structures of a hydrogen atom and a chlorine atom.
1. A hydrogen atom with one electron and a chlorine atom with 17 electrons
Molecules
Most covalently bonded substances consist of small molecules. A molecule is a group of two or more atoms joined together by covalent bonds. Molecules of the same element or compound always contain the same number of atoms of each element.
The atoms in a molecule are always joined together by a covalent bond. Substances that are made up of ions do not form molecules.
Sizes of atoms and simple molecules
A small molecule contains only a few atoms, so atoms and small molecules have a similar range of sizes. They are very small, typically around 0.1 nm or 1 × 10-10 m across.
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The rows in the top third - This group consists of elements like Sodium, Magnesium, Potassium and Calcium on the right and Chlorine, Carbon, Nitrogen and Oxygen on the left.
Sodium and Chlorine are components of salt, a very important compound of our blood, essential for transferring electrical signals from the brain to the rest of the body and vice versa. Calcium is the building block of our bones, while Magnesium and potassium ensure proper functioning of our organs.
Answer : Option D) The pH of the solution is 8.0.
Explanation : pOH of a solution is a measure of hydroxide ion 
concentration in a particular solution. It gives the measure of alkalinity of a solution. Normally, aqueous solutions at 25°C have pOH which is less than 7 are usually alkaline, when pOH is found to be greater than 7 then they are acidic and when pOH will be equal to 7 then it is neutral.
pH + pOH = 14, this relationship is used to find pH of any unknown solution with given pOH value,
Here, we known pOH is 6.0, so we get,
pH = 14 - 6 = 8.0;
Hence, the pH will be 8.0.
Human activities contribute to climate change by causing changes in Earth's atmosphere in the amounts of greenhouse gas- es, aerosols (small particles), and cloudiness. The largest known contribution comes from the burning of fossil fuels, which releases carbon dioxide gas to the atmosphere.
