What is the rule for how many significant figures you are able to get using a measuring instrument?

What three things determine the shape and size of a puddle when water is poured out onto a surface

Which metal exist in liquid state and can be cut with knife ?

Ammonium perchlorate nh4clo4 is the solid rocket fuel used by the u.s. space shuttle. it reacts with itself to produce nitrogen gas n2 , chlorine gas cl2 , oxygen gas o2 , water h2o , and a great deal of energy. what mass of nitrogen gas is produced by the reaction of 2.1g of ammonium perchlorate?