An instrument which measure relative humidity is a hygrometer
Scientists used the calculated density to determine that Mercury holds a large metallic core. Radar images taken from Earth revealed that the core is molten liquid, rather than solid. Mercury's core has more iron than any other planet in the solar system.
Answer;
- Oxygen
-Ancient cyanobacteria released oxygen, which assisted in creating the atmosphere as we know it today.
Explanation;
-The oxygen atmosphere that we depend on was generated by numerous cyanobacteria during the Archaean and Proterozoic Eras.
-Cyanobacteria are aquatic and photosynthetic, meaning they live in the water, and can manufacture their own food. During the process of photosynthesis, energy from sunlight is used together with carbon (iv) oxide and water to form organic molecules that serve as nutrients for the organisms and also oxygen gas is released to the atmosphere.
Answer: a) 
b) 
Explanation:
If percentage are given then we are taking total mass is 100 grams.
So, the mass of each element is equal to the percentage given.
a) Mass of Ba= 66.06 g
Mass of Cl = 34.0 g
Step 1 : convert given masses into moles.
Moles of Ba =
Moles of Cl = \frac{\text{ given mass of Cl}}{\text{ molar mass of Cl}}= \frac{34g}{35.5g/mole}=0.96moles[/tex]
Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.
For Ba = 
For O =
The ratio of Ba: Cl= 1:2
Hence the empirical formula is
b) Mass of Bi= 80.38 g
Mass of O= 18.46 g
Mass of H = 1.16 g
Step 1 : convert given masses into moles.
Moles of Bi =
Moles of O= 
Moles of H=
Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.
For Bi= 
For O =
For H=
The ratio of Bi: O: H= 1:3: 3
Hence the empirical formula is
A stationary front (or quasi-stationary front) is a weather front or transition zone between two air masses, when neither air mass is advancing into the other at a speed exceeding 5 knots (about 6 miles per hour or about 9 kilometers per hour) at the ground surface. On weather maps, it is shown by a solid line of alternating blue spikes pointing to the warmer air mass and red domes pointing to the colder air mass. If your talking about a weather front Hope this helped.
