Explanation:
Sodium and potassium are in the same group on the periodic table because they both have similar number of valence electrons (1 electron) in their shells
Na = 2,8,1
K = 2,8,8,1
The dry ice absorbs heat from the air in the flask and become CO2 gas directly. So the heat flow from air to dry ice. And the CO2 gas increase the amount of the air. Though the temperature decreases, the balloon still inflates.
One of the differences I can think of is that hydrogen is no longer listed as a group I element.
According to the mendeleev tables that I looked up, hydrogen is catorgrized as a group I element, along with Lithium, sodium, Potassium etc. However, nowadays, hydrogen does not belong to any groups in the periodic table. This is because there are arguments about whether hydrogen belongs to group I. Group I elements are all alkali metals, while hydrogen is not. However, some people says that hydrogen only have one outer shell electron so it should be in group I. Some people even say hydrogen should belong to group VII because it only needs one more electron in order to achieve the duplet of electrons.
Therefore as you may notice, hydrogen in modern periodic tables are put in the center of the periodic table on the top.
There are different techniques to reduce friction, similar to 1. Cleaning the surfaces 2. Including lubricants 3. expanding the temperature 4. wetting the surface 5. expelling polluting influences. Egyptian could have moved the square through water, which would be Fluid Friction, and makes it less demanding to move.
Answer
C. Difference in temperature
Explanation
According to thermodynamics, heat transfer occurs when heat from a high temperature reservoir moves to a low temperature reservoir. For heat to be transferred, the two objects should have different temperatures with one having more temperature than the other. Heat transfer in solids is by conduction, in fluids is by convection and by radiation.
