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.