`Ag and Cu` are below hydrogen in activity series, yet they are found in combined state. Why? 

Which metals found iin combined state in nature ? Why ?

Although aluminium is above hydrogen in the electrochemical series, it is stable in air and water Why?

Aluminium occurs in combined state in nature whereas gold is found in free state. Why?

Oxidation number is the charge which an atom of an element has in its ion or appears to have when present in the combined state. It is also called oxidation state. Oxidation number of any atom in the elementary state is zero. Oxidation number of a monoatomic ion is equal to the charge on it. In compounds of metals with non metals, metals have positive oxidation number while non metals have negative oxidation numbers. In compounds of two difference elements, the more electronegative element has negative oxidation number whereas the other has positive oxidation number. In complex ions, the sum of the oxidation number of all the atoms is equal to the charge on the ion. If a compound contains two or more atoms of the same element, they may have same or different oxidation states according as their chemical bonding is same or different. A compound of Xe and F is found to have 53.3% Xe (atomic weight =133). Oxidation number of Xe in this compound is

The Lyman series of hydrogen spectrum lies in the ultraviolet region. Why?

The normal activity of living carbon - containing matter is found to be about 15 decays per minute for every gram of carbon. This activity arises from the small proportion of radioactive ._(6)^(14)C present with the stable carbon isotope ._(6)^(12)C . When the organism is dead, its interaction with the atmosphere (which maintains the above equilibrium activity. ceases and its activity begins to drop. From the know half-life (5730 years.) of ._(6)^(14)C , and the measured activity, the age of the specimen can be approximately estimated. This is the principle of ._(6)^(14)C dating used in archaeology. Suppose a specimen from Mohenjodaro gives an activity of 9 decays per minute per gram of carbon. Estimate the approximate age of the Indus-Valley civilisation.

The following are some statements about normal hydrogen electrode a) when a 'Zn' electrode is in combination of NHE, Zn electrode acts as cathode b) when a ‘Cu' electrode is in combination with NHE, Cu electrode is the anode c) when a ‘Ag' electrode is in combination with NHE, Ag electrode is the anode d) when a chlorine electrode is in combination with NHE, chlorine electrode is the anode

Why are alkali metals not found in the free state in nature?