What was the reason for an increase in voters in 1828 than 1824? What led to the nullification crisis?

The main reason for the increase in voters was the fact that suffrage was expanded.  Many more people were allowed to vote in 1828 than in 1824.  This was part of the changes of the Jacksonian Era.

The nullification crisis came out of the Tariff of 1828.  The South disliked the tariff very much.  They felt it hurt them and helped only the North.  So they tried to nullify it -- to say it was illegal and they would not follow it.  So then there was a crisis about what to do if part of the country said that.