What is the difference between an alkali and a base.

Hint: Lewis gave the concept of acid and base according to electron pair acceptor and electron pair donor. According to Lewis: Lewis acids are the electron pair acceptor and Lewis base are electron pair donors.

Complete step by step solution:
Acids: Those compounds or solutions which can give hydronium ion or proton donor or electron pair acceptors and have pH range $0 - 7$, are known as acids.
Bases: Those compounds or solutions which are proton acceptor, can accept hydrogen ion or give hydroxide ion, or electron pair donor and have pH range $7 - 14$, are known as bases.
Difference between base and alkali are as:


Additional information:
There are so many factors by which we can decide whether a compound or solution is acidic or basic.
pH values: If the pH value is in between $0 - 7$ then the solution or compound will be acidic in nature and If the pH value is in between $7 - 14$ then the solution or compound will be basic in nature. And if the pH value is exactly seven then compound or solution will be neutral i.e. neither acidic nor basic in nature.
Electron pair acceptor and donor: This concept was given by Lewis. According to Lewis: Lewis acids are those substances or solutions which can accept electron pairs and Lewis bases are those substances or solutions which can donate electron pairs.
Arrhenius concept: According to Arrhenius: Acids are those compounds or solutions which can give hydrogen ion or hydronium ion in water and bases are those compounds or solutions which can take hydrogen ion or hydronium ion in water.
Bronsted-Lowry concept: This was based on the proton acceptor and proton donor. If a compound or solution is a proton donor then it is known as acids and if the solution or compounds are proton acceptor then it is known as bases.

Note: Acids are sour in taste and change the litmus colour from blue to red while bases are bitter in taste and change the litmus colour from red to blue. The neutral compounds are neither acidic nor basic in nature. They do not change the litmus paper colour.