How can a magnet be used to find direction

Which is the correct symbol for an isotope of iodine with 53 protons and 78 neutrons?

Assume you measured the mass of the cart to be (500 ± 1) g and the mass of the additional mass you put on the cart to be (500 ± 1) g as well. since the scale you are using in the lab cannot measure objects heavier than 600g you will have to sum up individual pieces and propagate the error. so what would be the mass and the standard error of the cart and the mass

The substances that are necessary for producing of certain hormones and that store and transport vitamins