GATE Questions

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An ionic bond is formed between two molecules when transfer of valency electrons take place between them. 

Covalent bonding occurs when pairs of electrons are shared by atoms. Atoms will covalently bond with other atoms in order to gain more stability, which is gained by forming a full electron shell. By sharing their outer most (valence) electrons, atoms can fill up their outer electron shell and gain stability.

Examples of compounds with covalent bonds ::

HCl, CO2, O2,... 

The resistivity of wire or the metal conductor is depend on the number density of free electrons in the conductor. so its mainly depends on nature of the material

Lord Cornwallis introduced the Permanent Settlement of Bengal in 1793.

The photoelectric effect pointed to the particle properties of light, which had been considered to be a wave phenomenon. Particles like electron and protons have both particle like and wave like behavior. Thus, according to de Broglie, all the material particles in motion possess wave characteristics. Although the dual nature of matter is applicable to all material objects but it is significant for microscopic bodies only.

Ans. 
53 - 345 ÷ 23 = 2 ×(?)
53 - 15 = 2 ×(?)
38 = 2 ×(?)
? = 19