After a particularly rainy spring, Kristen and Amanda could no longer bear to stay indoors and with the first sign of fair weather, ventured outside for a walk through the park. As they passed the jungle gym, they noticed that the iron monkey bars looked different. What can you do to pure, solid iron to chemically change it?
cut it
melt it
weld it
oxidize it

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

The ammonia molecule in the diagram has the observed bond orientation because

Which statement is true about the model of the electromagnetic spectrum a: it change the frequencies of light. b: it compare wavelengths of light. c: the color of light waves can be changed using the model. d: the intensities of light waves can be decreased using the model.