19. D
20. Sorry don’t know but if I had to guess it would be B
21. A because fluorine has a higher electronegativity
22. D
23. B
24. Again don’t really know but I would guess D
25. A
There aren't any ions on here, but it will be the ion with a charge of 2+; since electrons have a negative charge, losing one will cause a 1+ charge, losing two will cause a 2+ charge and so on.
Hope this helps :)
B the girls arm will act as a pulley
Density of unit cell is mathematically expressed as
D =
where, Z = number of atoms/unit cell = 4 (For FCC structure)
Atomic weight of Cu = 63.5 g
a = edge length = 351 pm = 351 X 10^-10 cm
Avagadro's number = 6.023 X 10^23
∴ Density of unit cell =
= 9.752 g/cm3
Now, for FCC structure a = √8 r
where r = radius of Cu
∴ r = a/√8 = (351 X 10^-10)/√8 = 1.24 X 10^-8 cm = 124 pm