Is 1GB RAM with integrated graphics sufficient for Unity 3D on 12.04?

I'd say 1GB is low, considering that you have 256MB of that dedicated to the integrated Intel graphics!!

What I mean is that, with 12.04 Unity, if you will be doing a decent amount of multitasking, you will start to notice lags with 1GB. Eg Firefox open with 5+ tabs along with 3-4 other programs running in the background, etc. (This is based on my own extensive experience with a 1GB machine).

A stock i386 install of 12.04 desktop with Unity 3D uses about 550-600MB of RAM after boot for me, excluding caches and with near-zero swap usage.

So I believe that an additional 1GB of RAM will almost certainly solve your problem. However, since RAM prices are at historical lows (should also be in Bangladesh), if you can afford it I suggest you "max out" with a 2GB module and future-proof your computer :)

Temporarily, if you do not game, I recommend reducing the integrated graphics share to 128MB. This shouldnt affect the user interface/Unity in any way.

1 GB is low but, do you know about zram ? It's a nice application to use your swap space more effectively. I would try it. On my pc this app does a very good job.

Here is the link of Zram

The minimum memory requirement for Ubuntu 12.04 is 384 MB of memory for Ubuntu Desktop. Some of your system memory may be unavailable due to being used by the graphics card. If your computer has only the minimum amount of memory, the installation process will take longer than normal; however, it will complete successfully, and the system will perform adequately once installed.