Results in an increase in the number of c-z bonds, where z is an element that is more electronegative than carbon (usually o, n, or x).

The number of C-Z (Where Z = O, N or X means halogen) depends upon the valence electron present in Z. There are mainly covalent bonds between the carbon (c) and other atom. For the covalent bond there needed equal share of electron to produce sigma bond and to generate pi bond there should be vacant or partially filled p-orbital. The electronic configuration of carbon is ., thus there are 4 valence electrons at carbon atom. The valence shell of oxygen (O), nitrogen (N) and halogen (x) posses 6, 5 and 7 electrons. The halogens mainly forms sigma bonds only as the other shells of the halogens are filled and they need 1 electron to fulfill the octet. On the other hand for C-N bond the number may be 3 as the nitrogen can form one sigma bond and two pi bonds, whereas oxygen (O) can form maximum 2 C-O bond as it can form one sigma and one pi bond. Thus the chrome of number of C-Z bonds is C-N > C-O > C-X.

i believe it is c.) 1575 j.