Which equation is an example of the synthesis reaction

cao+> caco3

2nacl --> 2na+cl2

hci+n aoh > nacl+h2o

mgl2+cl2 --> mgcl2+l2

c is having 4 valence electrons and is bonded to three hydrogens and one sulphur atom, therefore, the number of bond pair is equal to four. as all the valence electrons are used in forming the bonds so, there is no lone pair left on carbon.

s is having 6 valence electrons and is bonded to one other sulfur atom and one carbon atom, therefore, the number of bond pair is equal to 2. as only two valence electrons are used in forming the bonds so, four electrons are left. therefore, two lone pairs are present on s.