Which of the following is common to both eukaryotic and prokaryotic cells?
a-nucleus
b-nucleolus
c-plasma membrane

The correct answer is c. plasma membrane.

The main difference between the prokaryotic and the eukaryotic cell is the presence of nucleus. The eukaryotic cells have nucleus and the prokaryotic cells do not have the nucleus. The nucleolus is present inside the nucleus, in case, the nucleus is missing, nucleolus also does not exist, hence, it is absent in prokaryotes.

Plasma membrane is common in both types of cells, it forms the outer boundary of the cell and keep the cell isolated from atmosphere.

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.