In which of the following molecule all carbon atoms are in one plane.

detailed solution

Correct option is D

[Step 1]: In option (1) butane CH3−CH2−CH2−CH3  all four carbon atoms are SP3  hybridised and arranged tetrahedrally.[Step 2]:In option  (2) 1-butene CH2=CH−CH2−CH3 two carbons are SP2 and planar    arrangement other two carbons are SP3 and tetrahedral arrangement.[Step 3]:In option (3) 1,2-butadiene CH2=C=CH−CH3 three carbons are SP2 and  planar arrangement. One carbons are SP2 and tetrahedral.[Step 4]: (4) 1,3-butadiene CH2=CH−CH=CH2  all four carbons are SP2 and  planar arrangement.i.e all carbons are in one plane.