Question

difference between the flag hoisted by Congress on 31 December 1929 and our national flag

Answer 1

The Indian National Flag symbolises national pride and is one of the most respectable national symbols. the national flag is to be made up of khadi. It is is popularly known as Tiranga which means "three colours". The flag was same looking and had same colors, the material of the cloth was a little different than we use today. 

Answer 2

The Indian National flag symbolizes pride and one of the most respectable national symbols. It was called a "flag not only of freedom for ourselves, but a symbol of freedom for all people" 
As per Indian law the flag was to be made up of Khaadi and the usage of flag by private citizens was not allowed, they could only use them on the day of Independence or Republic day but later the rules were made little bit flexible and everyone could use the flag and even it was allowed to be printed on other fabrics as well, other than that of Khaadi. 
The flag is known as 'Tiranga' which literally means three colors which is why the flag consists of three colors. It is in a horizontal shape with deep saffron color at the top, white in the middle and green at the bottom and at the centre of the white part there is a wheel which has 24 spokes in navy blue color which indicates the wheel of law (dharma chakra)