Xcode installation problem

As a development platform a 121 GB MBA doesn't offer much space to begin with, but I assume you knew that already.

You need to methodically review each of those categories and delete files that are not essential to using Xcode. The obvious large categories to examine are Documents and "Other". For a description of "Other" and what you can do about it, please determine if the following User Tip has any suggestions for you: What is “Other” storage on a Mac, and how can I clean it out?

Please bear in mind that I do not use any of the products mentioned in that User Tip, so I am unable to vouch for their effectiveness or determine their suitability for your purposes. Its principles are correct though, in that it's up to you to identify and delete what you can delete while maintaining the bare essential needs for that MBA... which is certain to be a challenge if you need to use Xcode for development purposes.

Another possibility that may be an option for you is to replace that MBA's internal storage module, assuming it is removable and that replacements are available. Doing that is not an approved hardware modification though—meaning you will invalidate whatever AppleCare warranty may still apply to that MBA and that you are willing to forfeit any authorized Apple service for it.

Nishvi wrote:

I have 20 Gb of space in my MacBook air still I am not able to install Xcode that's of 11.3 Gb.

11.3 GB is only the downloaded file size. Once installed, the Xcode app itself occupies over 30 GB on the Mac I happen to be using at present.

How to resolve this ??

How to free up storage space on your Mac - Apple Support