Explanation:Valency: It is the combining capacity of an element to form bonds by sharing electron pairs to make stable chemical compounds.Stability: It is the property of resistance of a molecule or compound to not react with other molecules, elements and compoundsImportant Points Magnesium:Magnesium is an element with the atomic number 12.It has the symbol Mg.It is a metal and thus its valency is +2.Its melting point is 650°C and its boiling point is 1090°C.Magnesium is the eighth-most abundant element.Nitrogen:Nitrogen is non-metal with atomic number 7.It occurs in gaseous form as dinitrogen.It has electronic configuration 1s22s22p3.Its valency is either -3 or -5.Its melting point is -210°C and its boiling point are -195.8°C.Silicon:Silicon has atomic number 14.It is represented with the symbol Si.Its melting point is 1410°C and its boiling point is 3265°C.It shows the valency of -4 or +4.Neon:Neon is a colourless, odourless and tasteless inert gas.Neon is chemically inactive due to its stable configuration.It is represented by Ne.Its valency is zero.Order of valencies:Ne < Mg < N < Si