For Android

Icons Resolution (Curved Edges):

48 × 48 (mdpi)
72 × 72 (hdpi)
96 × 96 (xhdpi)
144 × 144 (xxhdpi)
192 × 192 (xxxhdpi)
512 × 512 (Google Play store)
64 x 64 (tvdpi) (optional)

Splash screen Resolution:

Portrait:
200 x 320 (ldpi)
320 x 480 (mdpi)
480 x 800 (hdpi)
720 x 1280 (xhdpi)
960 x 1600 (xxhdpi)
1280 x 1920 (xxxhdpi)
1024 x 500 (Leaderboard)


Landscape (If your application enable in Landscape mode):
320 x 200 (ldpi)
480 x 320 (mdpi)
800 x 480 (hdpi)
1280 x 720 (xhdpi)
1600 x 960 (xxhdpi)
1920 x 1280 (xxxhdpi)


For IOS

Icon:
1024 x 1024
512 x 512

SplashScreen:
640 x 960
640 x 1136
750 x 1334
768 x 1024
1242 x 2208
1536 x 2048
1080 x 1920
Note: All Images should be in .png format.