Barium, Beryllium, Radium, and Calcium.
<h3>Explanation</h3>
All four metal elements (Ba, Be, Ra, and Ca) are found in group 2 of a modern periodic table. By periodicity, they have similar chemical properties.
Shared properties likely include:
- Softness. With only two valence electrons per atom, the four elements form weak metallic bonds. Their pure forms are thus easy to shape and cut.
- High reactivity. Group 2 "alkaline-earth" metals are only two electrons away from ideal gas electron configurations. They lose electrons more readily than most transition metals such as iron and copper do. Group 2 metals tarnish easily in the earth atmosphere, and reacts readily with water to produce hydrogen and a base- hence the name "alkaline."
Sound waves are waves of growing larger and smaller, making it seem elastic through substances, such as air.
Answer : The number of molecules present in nitrogen gas are, 
Explanation :
First we have to calculate the moles of nitrogen gas by using ideal gas equation.
where,
P = Pressure of 
gas = 
(1 atm = 760 mmHg)
V = Volume of gas = 985 mL = 0.982 L (1 L = 1000 mL)
n = number of moles = ?
R = Gas constant = 
T = Temperature of gas = 
Now put all the given values in above equation, we get:
Now we have to calculate the number of molecules present in nitrogen gas.
As we know that 1 mole of substance contains 
number of molecules.
As, 1 mole of gas contains number of molecules
So, 
mole of gas contains 
number of molecules
Therefore, the number of molecules present in nitrogen gas are,
pretty sure it's both are physical changes.
Elements and compounds are both examples of pure substances. Compounds are substances that are made up of more than one type of atom. Elements are the simplest substances made up of only one type of atom. i hope that helps:)
