How is a `sigma` (sigma) bond formed?

Sigma bonds are :

A molecule (X) has (i) four sigma bonds formed by the overlap of sp^(2) and s orbitals, (ii) one sigma bond formed by sp^(2) and sp^(2) orbials and (iii) one pi bond formed by P_(z) and P_(z) orbitals. Which of the following is X?

A molecule (X) has (i) four sigma bonds formed by the overlap of sp and s orbitals (ii) one sigma bond formed by sp and sp orbitals and (iii) one bond formed by and p, orbitals. Which of the following is X?

In which of the following molecules, sigma bonds formed by the overlap of sp^3 d and P orbitals are absent ?

How many sigma bonds and pi bonds are there in the formation of N_2 molecule ?

How many sigma and pi bonds are present in acetylene molecule?

How many sigma and pi bonds are in O_2 molecule?