PLEASE HELP! Which of the following is an example of a chemical change?

A. A large nail rusting
B. Folding a piece of paper
C. Filling a balloon with hot air
D. Wax melting from a candle

7. what temperature is need to just dissolve 50 g of nh4cl in 75 g of water? '

Which of the following did jj thompson discover about atoms? a)an atom has an internal structure. b) atoms are tiny indivisible particles. c)electrons orbit the nucleus of an atom. d) the nucleus of an atom contains protons and neutrons.

Agroup of students is studying convection current. they fill two identical balloons with the same amount of helium. one balloon is placed in a freezer and the other is in an area with warm air. after 10 minutes, the balloon are released from a height of 1 meter. which of the following to the students most likely observe? a) the warm balloon expands and rises. the cold balloon shrinks and sinks b) the balloon both rise. the cold balloon is larger than the warm balloon c) the cold balloon expands and rises. the warm balloon shrinks and sinks d) the balloon rise at the same rate. both balloons are the same size