Kari needs to change the brightness and contrast on an image she has inserted into a word document.

which group should she use to do this?

adjust
picture styles
arrange
size

Adjust

Explanation:  

For changing contrast and brightness of any image in Word document, Adjust group is used which is found in Format tab. These formatting feature for adjustment of image is found under Picture Tool option. Level of brightness and contrast can be set accordingly by moving the thumbnail's bar. Other options are incorrect because Picture style is used for adding style to the image .Arrange option is used for organizing the image in order.Size is used for adjusting the measurement of image.Thus , the most appropriate option is adjust.