What was observed that led to the arrangement of sixty-three already- known elements by increasing atomic weights in the periodic table?

What is the number of moles of chemical units represented by 9.03x10^24? and how do i show work? (dumb it down )

Liv sheldon given the balanced equation for an organic reaction: c2h2 + 2cl2 → c2h2cl4 this reaction is best classified as *

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