Which of the following groups contains entirely linear molecules?

The group that contains entirely linear molecules is (d) CO₂ H₂ N₂. To determine if a molecule is linear, we need to examine its molecular geometry. Linear molecules have a symmetrical arrangement of atoms around a central atom, with a bond angle of 180 degrees. In group (a), H₂NH₃O₂, the molecule contains different atoms (hydrogen, nitrogen, and oxygen) that cause an asymmetrical arrangement and do not have a bond angle of 180 degrees, so it is not linear. In group (b), CO₂NH₃₂, the molecule contains a non-central nitrogen atom that disrupts the symmetry and does not have a bond angle of 180 degrees, so it is not linear. In group (c), H₂CH₄N₂, the molecule contains different atoms (hydrogen, carbon, and nitrogen) that cause an asymmetrical arrangement and do not have a bond angle of 180 degrees, so it is not linear. In group (d), CO₂H₂N₂, both molecules contain only one type of central atom (carbon and nitrogen, respectively) and no lone pairs of electrons, which allows for a symmetrical arrangement of atoms and a bond angle of 180 degrees, making them both linear. In group (e), CH₄O₂CO₂, the molecule contains different atoms (carbon, hydrogen, and oxygen) that cause an asymmetrical arrangement and do not have a bond angle of 180 degrees, so it is not linear. Therefore, the group that contains entirely linear molecules is (d) CO₂H₂N₂.