a distinct lipo polysaccharide layer is found in

1. gram (+) bacteria
2. gram (-) bacteria
3. all bacteria
4. mycoplasma

The correct option is 2.
Gram-negative bacteria are a class of bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation, making positive identification possible. The thin peptidoglycan layer of their cell wall is sandwiched between an inner cell membrane and a bacterial outer membrane. In Gram staining, the outer lipid-based membrane of gram-negative bacteria is removed by an alcohol solution. The alcohol also decolorizes the then exposed peptidoglycan layer by dissolving away the previously applied crystal violet. A counterstain (safranin or fuchsine) is then added which recolorizes the bacteria red or pink.

Gram-positive bacteria on the other hand have a thicker peptidoglycan layer in their cell wall outside the cell membrane, which retains the crystal violet stain during the alcohol wash, so long as it is timed correctly. The counter stain may also be absorbed by gram positive bacteria but the darker crystal violet stain predominates visually.