For the reaction C+2H 2 —->CH 4 calculate the percent yield if 98 g of methane is produced when 100. g of carbon reacts with an excess of hydrogen?

Can someone me with questions 12 and 13 plz.

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

What does the symbol (–hfus) indicate in a phase change?