Explain the term inductive effect.
Whenever an electron - withdrawing atom such as halogen i.e. - X(or a group such as nitro) is attached to the end of a carbon atom, the σ; electrons of the C – X bond are displaced towards the more electronegative halogen atom. As a result, the atom X acquires a partial negative charge (δ–). C1 on the other hand acquires a partial positive charge (δ+). The C1 –X bond thus becomes a polar bond.
The partial positive charge on C1, in turn, attracts, the σ;-electrons, of the C1 – C2 bond towards it. As a result, C2 acquires a partial positive charge (i.e. δ'+ ), of course, smaller than that of C1. Similarly, C3 will acquire a small positive charge (δ"+ ) that will still be smaller than that on C2. Thus, positive charge (δ"+ ) that will still be smaller than that on C2. Thus, positive charge (δ"+ ) that will still be smaller than that on C2. 
This permanent displacement of electrons along the chain of carbon atoms due to the presence of an atom or group of different electronegativity at the end of the carbon atom is called inductive effect or I-effect. It is represented by an arrow as shown below:
The atom X exerts an inductive effect only up to a certain length of the chain depending upon its electronegativity. Beyond that, the effect disappears. For practical purposes, it is ignored after the third atom.
The inductive effect is also called transmission effect (T-effect) because the polarity is transmitted along the carbon atom chain.
Types of Inductive effect. It is of two types:
(i) - I effect (Electron withdrawing inductive effect). If the substituent attached to the end of the carbon chain is electron withdrawing, the effect is called - I effect. For example,
The decreasing order of -I effect of some common groups is as follows:
(ii) + I effect (Electron releasing inductive effect). If the substituent attached to the end of the carbon chain is electron donating, the effect is called +I effect. For example. 
The decreasing order of some groups having +I effect is as follows:
