Which of the following compounds contain all the carbon atoms in the same hybridisation state?

Correct answer: 1 and 4) 

Concept:

• Hybridisation is a process in which two or more atomic orbitals of comparable energy of the valence-shell of an atom (central atom of the molecule or ion) either in its ground state or in its excited state mix together and give rise to the formation of new degenerate orbitals which are called hybrid orbitals. 
• carbon is said to be sp² hybridized when it is Doubly bonded with any 1 atom and  Singly bonded with any other 2 atoms.
• We know that when a carbon atom is sp² or sp hybridized, all the atoms attached to it are in a plane.

Explanation:

• If the carbon is connected to four other atoms, its hybridisation is sp³ ( number of atoms = sum of the superscripts; 1 for s and 3 for p; 1+3 = 4).
• If the carbon is connected to three other atoms, its hybridisation is sp² (number of atoms = sum of the superscripts; 1 for s and 2 for p; 1+2 = 3).
• If the carbon is connected to two other atoms, its hybridisation is sp  (number of atoms = sum of the superscripts; 1 for s and 1 for p; 1+1 = 2).
• Hybridization of carbon atoms in different compounds is shown below:

• In options 1 and 4, all carbon atoms are in the same hybridisation state, which is sp and sp² hybridised, respectively.

Conclusion:

Thus, In options 1 and 4, all carbon atoms are in the same hybridisation state, which is sp and sp2 hybridised, respectively.