Question

question 1
which statement is correct?
a double bond consists of two single bonds
a double bond consists of one sigma and one pi bond.
a double bond consists of two sigma bonds.
a double bond consists of two pi bonds.

Explanation:

In chemical bonding, a single bond is a sigma ($\sigma$) bond. A double bond is formed when one $\sigma$ bond (from head - on overlap of atomic orbitals) and one $\pi$ bond (from lateral overlap of atomic orbitals) are present between two atoms. A single bond is not the same as a part of a double bond in terms of orbital overlap nature. Two $\sigma$ bonds cannot form a double bond as the geometry and orbital overlap would not be correct. Two $\pi$ bonds alone also cannot form a stable double bond as a $\sigma$ bond is required for the initial strong connection between atoms.

Answer:

A double bond consists of one sigma and one pi bond.