Based on the standards of units conversion, to convert from micrometer to meter, we multiply by 10^-6.
Since we there is a square (10^2) to consider, then to convert from micrometer squared to meter squared, we will multiply by (10^-6)^2 as follows:
1.5 <span>μm2 = 1.5 x (10^-6)^2 = 1.5 x 10^-12 meter sqaures</span>
The compound formed by chlorine and barium is 
as the number of valence electrons in barium is 2 and in chlorine is 1. In this compound, barium acts as a cation and chlorine acts as an anion. The formation of the compound is as shown in the image.
Since, barium is an element of Group-2 (alkaline earth metal) so the other element that has a chemical formula most and least similar to the chemical formula of the compound formed by chlorine and barium should be from Group-2 (alkaline earth metal) only which has properties somewhat like barium. So, the element is strontium.
Strontium forms a compound with formula 
in which strontium acts as a cation and chlorine acts as an anion. The formation of the compound is as shown in the image.
Carbon will have 4 valence electrons. It will have 2 in the p orbital and 2 in the s orbital. You can see this when you find the noble gas configuration of carbon which is [He]2s²2p² showing that carbon has 4 valence electrons.
I hope this helps. Let me know if anything is unclear.
The interaction between the atoms is due to number of electrons in the valence shell
