Here is a link to a website that explains these observed trends.
https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book%3A_Introductory_Chemistry_(CK-12)/06%3A_The_Periodic_Table/6.15%3A_Periodic_Trends%3A_Atomic_Radius
Answer:
A. They must be kept separate from moisture and oxygen
Explanation:
Alkali metals refers to a group of chemical elements in the periodic table. It is the common name given to Group 1 elements (excluding hydrogen). They are generally metallic in nature with physical properties like shining lustre, silvery in appearance etc. Alkali metals include lithium, Pottasium, Sodium, Rubidium etc.
One important chemical property of alkali metals is their high reactivity i.e. they tend to react quickly with other substances. For example, alkali metals react vigorously with water to form hydroxides. They also react with oxygen to form oxides. Due to this highly reactive properties, they are kept or stored away from moisture (water) and oxygen (present in air).
Explanation:
Let us assume that volumes is equal to spheres volume of nucleus.
fm = femto meter = 
pm = pico meter = 
Hence, calculate the volume as follows.
V = 
= 
= 82.4481 
(cubic femtometers)
or, = 82
Now, we will calculate the volume of the atom as follows.
V =
= 
= 1436758.4 
(cubic picometers)
thus, we can conclude that volume of the nucleus is 82 and volume of the atom is 1436758.4 .
The elemental symbol of gold is denoted on the periodic table as being Au.
