How many total atoms are in one molecule of cobalt hydroxide?

Joan writes four numbers on the board in standard form, and then she writes their scientific notation

For the reaction shown, calculate how many moles of no2 form when each of the following completely reacts. 2n2o5(g)→4no2(g)+o2(g) part a 1.0 mol n2o5 express your answer using two significant figures. nothing mol m o l request answer part b 5.4 mol n2o5 express your answer using two significant figures.

Why is the melting of ice a physical change ?