The element sodium (Na) occurs naturally as a light solid with a shiny, metallic appearance. When sodium is added to water, the sodium catches on fire, moves violently, and breaks the glass dish. This indicates that the properties of the elements in the same column on the periodic table as sodium(Na) have-
A. the tendency to be highly reactive
B. brittle textures which disintegrates in water
C. properties of metals and non metals
D. a full octet of eight electrons in the outer shell

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.