Questions

A 40% solution of Formaldehyde known as Formalin is used in the preservation of biological specimens because of its hardening action on proteins. 

The American noncommissioned officer tradition began with creation of the Continental Army in 1775 at the beginning of the American Revolution. They adopted NCO traditions from French NCO.

An invention that improved safety for railway passengers is Air brakes. With the use of air brakes using compressed air, become more effective by preventing many train accidents.

India was one of the main centres of world trade and industry. Peter the Great of Russia was led to exclaim: “Bear in mind that the commerce of India is the commerce of the world and ... he who can exclusively command it is the dictator of Europe.”

DPT refers to a class of combination vaccines against three infectious diseases in humans: diphtheria, pertussis, and tetanus.

Pertussis refers to whooping cough.

Free memory is maintained in linked lists, each of equal sized blocks. Any such block is of size 2^k. When some memory is required by a process, the block size of next higher order is chosen, and broken into two. Note that the two such pieces differ in address only in their kth bit. Such pieces are called buddies. When any used block is freed, the OS checks to see if its buddy is also free. If so, it is rejoined, and put into the original free-block linked-list.