Lanthanides series ranges from Thorium to.…
a) Barium
b) Thorium
c) Lawrencium
d) Lutetium
The rarest naturally-occurringelement in the earth’s crust is………….
a) Sodium
b) Astatine
c) Calcium
d) Boron
Explanation:Astatine is a chemical element with the symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. Astatine is likely to have a dark or lustrous appearance and may be a semiconductor or possibly a metal.
The earth crust appears to contain about ……. of Astatine.
a) 20g
b) 38g
c) 28g
d) 48g
Groups:
The vertical columns of elements in the periodic table are called ……….
a) periods
b) blocks
c) groups
d) none of these
Atoms having the same number of valence of electrons are present in the same ………
a) period
b) group
c) block
d) all of these
