Which is better conductor of electricity aluminium or copper and why?

Copper! It's like the Usain Bolt of electrical conductivity among common metals. Copper is a much better conductor than aluminum, with a conductivity of around 5.96×10^7 S/m compared to aluminum's 3.5×10^7 S/m. 

Why is copper such a great conductor? It's all about those free electrons! Copper has one valence electron that's just itching to move around, creating a strong repelling reaction in other electrons. This means it takes very little resistance for an electric current to flow through copper.

Aluminum, on the other hand, is like the tortoise in this race. It's a decent conductor, but it just can't keep up with copper. Aluminum has three valence electrons, which makes it harder for an electric current to flow smoothly.

So, if you're looking for a metal that's a whiz at conducting electricity, copper is your go-to metal. Just remember, with great conductivity comes great cost - copper is more expensive than aluminum. But hey, you get what you pay for, right?