A linear shape is one in which the atoms are arranged in a straight line. Some examples of molecules or ions with a linear shape include:

1) Carbon dioxide (CO2): The carbon atom is bonded to two oxygen atoms in a linear arrangement.

2) Hydrogen cyanide (HCN): The hydrogen atom is bonded to the carbon atom, which is in turn bonded to the nitrogen atom in a linear fashion.

3) Nitrogen gas (N2): The two nitrogen atoms are bonded to each other in a linear arrangement.

4) Acetylene (C2H2): The two carbon atoms are bonded to each other and each carbon atom is bonded to a hydrogen atom in a linear arrangement.

These are just a few examples of molecules or ions that have a linear shape. There are many other molecules and ions that can adopt a linear shape depending on their electronic structure and bonding.