For electronic chips, surface defects may considerably affect their performance. A two$-$atomic layer terrace

is formed on $(001)$ plane of $Ag$ surface $($in blue$).$ The lattice constant atomic bond energy of $Ag$ are a and

${}_b,$ respectively.

What is the excess energy of this terrace?

What does the excess energy mean to the formation of the terrace?

Does this terrace influence surface adsorption? Why?