atarajput,

There are no Windows 7 32 bit drivers available for download. There are Windows 7 64 bit at the link  below. You can also add your service tag number on the site and be presented with the list of drivers for your computer.

Dell Drivers and Downloads Inspiron 3521

there are drivers available for win-7(32 bit) in the website

123driver-laptop.blogspot.in/.../dell-inspiron-3521-drivers-for-windows7.html

check them out