what is resonance,inductive effect,electromeric effect and hyperconjugation?

Dear Shubhi,

Please post one question at a time.

Answer to your first query is given below.

(a)  Resonance or mesomeric effect: If a molecule is assigned two or more Lewis structures, none of which is capable of describing all the known properties of the compound, then the actual structure is intermediate or resonance hybrid of these structures. This phenomenon is called resonance. The various structures written are called resonating structures.

Example: Resonating structures of CO₂ are shown below

Resonance effect is classified as +R effect and −R effect

• If a substituent has tendency to donate electrons to double bond or conjugated system, then the effect is called the positive resonance effect or +R effect. Groups such as  show +R effect.
• If a substituent has tendency to withdraw electrons from a double bond or conjugated system towards itself, then the effect is called the negative resonance effect or −R effect. Groups such as  show −R effect.