Which of the following tools and activities would measure muscular endurance? pedometer during a mile run test stop watch to count the number of pull-ups performed

Using a pedometer during mile run.  

You're doing a mile run, which helps with cardiovascular endurance. That isn't muscular endurance, so cross that off.

Using a ruler to measure sit and reach results.  

If you feel the tension or pain in your legs and back, that's flexibility, so this is not the right one either.

Using a scale to measure body weight.  

I do not think this is even a type of exercise. You're just measuring your BMI and weight when you do this kind of thing.  

I'd say it's "Using stop watch to count number of pull-ups."  

I think it is this one because, everyone's body is different.