How does calcium oxide act as Lewis base? Please explain with Lewis dot strucutre.

@ rachana 
cao is a electron pair donor , so, we can call that as a lewis base . 
acc to the defination a lewis acid can be defined as an electron pair acceptor . and lewis base which can donate a electron pair . 
if u can take it to simple level , an OH- ions has an electron pair around the oxygen which is what makes it an negative ion , this can bind with H + and make its a +ve ion as h+ dnt have any electron 
so, applying the above principle , the oxide ion in cao donate an electron pair to C to form a bond between two reactants , forming the product 
HOPE IT CLEARS 
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