It sounds like you're asking "Which PPI value do I use in PhotoShop when creating images for the web".
The answer is: It doesn't matter.
Image resolution in PhotoShop only affects printing the image. It has no affect on the image when displayed in a web browser. All that matters is the pixel dimensions of your image. If your image is 100px x 100px, regardless if you set it at 72ppi or 300ppi, it will look exactly the same on screen.
Most people use 72ppi which is a fine, acceptable default, but it really has no bearing at all on the final output.
The only other time that resolution will likely come in to play is if you need to support high ppi devices--at which point you'd need to create an image with double-the-size dimensions.
So if you want a high resolution image for a Retina iPhone, you'd need to create a 200px x 200px version of your earlier image.