IF I DO AN IMAGE in FW or PS of 320PPI - 5cm x 5cm, and the mobile app that this image appear runs on a mobile phone of 200ppi display resolution, then resolution seem of image should be 200ppi ... in other words should adapt automatically???
It depends on how you have the layout. If you put the image on a 'wrap content' view the view will size to the number of pixels in the image. If you give a specific size or a size relative to the parent then the view will be set to the specific size, and depending on the scale type could be scaled down or clipped. See http://developer.android.com/reference/android/widget/ImageView.ScaleType.html
in hybrid apps html5...well if image(<img src="file.jpg" width="250" />) is bigger resolution ratio(ppi) than screen is or vice versa, the quality of image will be that of smaller resolution ratio of the two??? yes correct / No...
edit: I take that back - I have some guesses. The image can never be displayed at a higher resolution than the screen (physical limit of the screen). My guess is if the width you define is smaller than the number of pixels in the image, the image will be scaled down to fit the width you define, but if the size is larger than the number of pixels in the image the image will be scaled up. In an HTML tag the width is defined in pixels, not inches or relative units, so ppi is not relevant.
Of course, that means the image will take up different physical sizes depending on the screen it is on. 250 pixels on a low resolution phone may fill 50% of the screen or more, but on a high resolution screen may only fill 30% or less. Your framework to build your 'hybrid HTML5' app may do something to maintain size across multiple screen resolutions, but to figure out what it does you will need to read their docks.
p.s. Your question is "is it a or is it b? Answer yes or no." Typically the answer to these types of questions are 'yes, is either a or b' which usually isn't very helpful. I think in your case, though, the two options you give are both wrong, the answer is no: it is neither using the higher resolution nor the lower resolution, but will use some density depending on size of the original image (in pixels, not density) and the size of the width you define.