• # question_answer What order of $C-H$ bond lengths do you expect in ${{C}_{2}}{{H}_{6}},\,{{C}_{2}}{{H}_{4}}$ and ${{C}_{2}}{{H}_{2}}$ and why?

$C-H({{C}_{2}}{{H}_{6}})>C-H({{C}_{2}}{{H}_{4}})>C-H({{C}_{2}}{{H}_{2}}).$ This is because hybrid orbitals of carbon involved in overlapping with 1 s orbital of hydrogen are $s{{p}^{3}},\,s{{p}^{2}}$  and sp respectively and their sizes are in the order $s{{p}^{3}}>s{{p}^{2}}>sp$ .