To determine the maximum number of coplanar atoms in propadiene (CH₂CCH₂), we need to consider the molecular structure and identify the atoms that can exist within the same plane.
Propadiene has a linear structure, with two carbon atoms (C) connected by a double bond and two hydrogen atoms (H) attached to each carbon. The double bond creates a rigid structure that prevents free rotation around it.
In propadiene, the two carbon atoms and the double bond between them lie in the same plane. The hydrogen atoms, however, are attached to the carbon atoms and extend out of the plane.
Therefore, in propadiene, only the two carbon atoms and the double bond are coplanar. The maximum number of coplanar atoms in propadiene is three: the two carbon atoms and the double bond between them. The four hydrogen atoms are not coplanar with the carbon atoms and the double bond.