Determine the oxidation number of the element that is underlined within the compound.
li2sio3
о +2
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Explanation:

Oxidation number

It is defined as “residual charge that is present on atom when the atom is in combined state with other atoms”.

Rules to assign and calculate oxidation number  

1.The oxidation number of atoms in their elemental state is taken as zero.  

2.The oxidation number of mono-atomic atoms like Na+ etc is taken as 1.  

3.The oxidation number of Hydrogen is +1 when present with non metals and -1 when present with metals.  

4.The oxidation number of oxygen is -2 in most of the compounds but in peroxides it is -1.

5.The metals always have oxidation number in positive and non metal in negative when present together in ionic compounds.

6.In compounds that have two atoms with different electro negativities, the oxidation number of more electronegative is taken as –ve and for less electronegative it is taken as positive. For example: In OF2 the oxidation number of oxygen will be in positive and oxidation of fluorine will be in negative.  

7.In neutral compounds, the sum of all oxidation numbers is equal to zero.

8.In complex ions, the sum of oxidation states of all the atoms is equal to the charge present on the complex.  

So, following these rules we can find the oxidation states for all the elements above :

The compound given is :

Li₂SiO₃

Let us find for lithium first :

x      +4       -2

Li₂    Si       O₃

2x + (4) + -6 =0

2x-2 =0

2x =2

x=2/2

x=+1

Let us find the oxidation state for Silicon

+1         x     -2

Li₂       Si       O₃

+2 + x -6 =0

x-4 =0

x =+4

Let us find for oxygen

+1       +4       x

Li₂     Si      O₃

2+4 +3x =0

6 + 3 x =0

6=3x

or , x=6/3 =+2