Hey @Bishal Tim firstly I would recommend not using images in RTE but instead creates image blocks. The reason is you will have full control over image blocks and apply different responsive rules based on what areas they are used in and whether or not you wish to allow the Editors to only add them specific ratios or to allow it to be fully responsive if the users have the freedom to add different ratios and crops.
With that said to address the question you are asking you can make images responsive in rte's but it is quite a lot of work to ensure that they remain resizable and keep that aspect ratio at different crops.
Fortunately CSS aspect ratio is now widely supported and will certainly help. Where I have been asked to ensure that images in RTE perform responsively I have created separate sets of CSS rules based on an ID for each of the rte's depending on where they are placed and how they need to react on different devices.
Again my strongly said advice would be to create separate blocks for images in which you can create many variations with full control over how they respond I hope that helps.