Molecules having all atoms lying in the same plane is c) HCN
HCN is a molecule in which all the atoms in the same plane i.e. it is a Planar molecule.
A Planar molecule is the one in which atoms are arranged in same plane i.e. atoms arrange themselves to exist in a two dimensional plane around the central atom.
The presence of double bond or triple bond in a molecule allows the molecule to get arranged in a plane.
The presence of triple bond in HCN allows it to be arranged in a plane.
HCN to be specific is a Linear molecule in which the angle between H and CN is 180.
The bond between C and N atom is a triple bond containing two pie bonds and one sigma bond.
Hence c) HCN is a planar molecule.
Learn more about Planar molecule here, https://brainly.com/question/14019685
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