The percentage composition of oxygen in the compound ca(clo3)2 is approximately

assume you have 1 mole (or any other number, it doesn't matter). Mass = 206.98 g/mole. This is straight from the molar mass so that's why I like to use 1 mole  

From the chemical formula, 1 mole of Ca(ClO3)2 contains 6 moles of oxygen atoms.  

Mass of 6 moles of O atoms = 6 moles * 16 g/mole = 96 g  

mass % oxygen = 96 g / 206.98 g * 100 = 46.4%.  

You could also do it on a mole percent. 1 mole of Ca(ClO3)2 contains 9 moles of atoms.  

6 moles of these are oxygen atoms so the mole % = 6 moles / 9 moles * 100 = 66.7 mole %

If you mean percent by weight or percent by composition? Ca(ClO3)2 is 67% O by composition (number of atoms) and, as calculated by Ricki, 46% by weight.

the electronic configuration of an atom with eight electrons is 1s²2s²2p⁴. the orbital diagrams are shown in the figure.

as per the hunds rule:

1. electrons tend to avoid being in the same orbital as per as practicable.

2. electrons in different orbitals of the same energy will have their spin parallel.

this can be illustrated from the multiplicity of the orbitals of the atom. as there are four electrons in the p orbital and p orbital has 3 sub-shells. the electrons can be fed in different ways as shown in the figure but the correct orbital diagram will be as per the hunds rule.

atomic number of carbon is 6

electronic configuration of carbon is 1s²2s²2p²

orbital diagram of carbon is as shown here in the image.