Question

how ethane has 7 covlaent vonds

Answer 1

U can easily identify the number of bonds by seeing it
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one bond among the two carbons and other six with hydrogen 
all together 7 bonds

Answer 2

here below is your answer and the picture is above which will help you -

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in the diagram , C denotes carbon atom and H denotes an hydrogen atom .

as – sign denotes a single bond , so on counting the total bonds , we get that ethane has 7 bonds in total .

as we can see , there are 3 bonds with both the carbon atoms , and one which joins both carbon atoms

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