Which number indicates the energy level of an atom's valence electrons? O A. The period number
O B. The group number
O c. The atomic number
O D. The mass number

Given sno2 + 2h2 - sn + 2h20 tin oxide reacts with hydrogen to produce tin and water. how many moles of sno2 are needed to produce 500.0 grams of sn?

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 is the temperature of 0.750 mol of a gas stored in a 6,850 ml cylinder at 2.21 atm? . 2.95 k 5.24 k 138 k 246 k