The constituent particles of atom are called sub atomic particles. Therefore electron, proton and neutron are sub atomic particles. Later it was understood that protons and neutrons are made up of quarks. These quarks are also sub atomic particles. Recently it is discovered that the Higgs particles or God particles give mass to many particles like protons, neutrons etc.

Black holes are end stage of stars whose mass ranges from 20 times to 1 million times the mass of the sun. Because of their dense mass, they have very strong gravitational force such that no particle or even light can escape from it. Therefore they are not visible to human eye. Every galaxy has black hole at its center. 

Robots are automated machines which have many mechanical parts like wheels, arms, fingers, legs etc. Therefore a strong material is needed. For a given size, steel has several times stronger.

Advantages of Robotics:
(i) Robots are more precise and error free in performing the task.
(ii) Robots never get tired like humans. It can work for 24 x 7. Hence absenteeism in work place can be reduced.
Disadvantages of Robotics:
(i) Unemployment problem will increase.
(ii) Robots can perform defined tasks and cannot handle unexpected situations.

(i) If the particle of a solid is of size less than 100 nm, it is said to be a nano solid, if the particle size exceeds 100 nm, it is a bulk solid.
(ii) Both have same chemical properties. But their mechanical, electrical, optical, magnetic properties differ.