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3 years ago

According to scientific evidence, earth’s earliest atmosphere lacked oxygen. Over time, oxygen was added to the atmosphere.

1 answer:

4 0

B.
The cynobacteria were already there without the oxygen, so that rules out A, and a lot of prokaryotes were anaerobic, so that rules out C. Finally, Photosynthesis does not require oxygen. Instead, Oxygen is a waste product of it. Therefore, it cannot be D. So, we are only left with B
Hoped this helped :D

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Find the molarity: 9.82 grams of lead (IV) nitrate are dissolved to make 465 mL of solution.

solmaris [256]

Molarity is moles per liter. Therefore you must covert grams->moles by dividing 9.82 by the molar mass of lead IV nitrate. Then convert mL->L. Once you have those two numbers you can plug them into the formula Molarity = mol/L.

3 0

3 years ago

A certain liquid X has a normal freezing point of 7.60 °C and a freezing point depression constant K= 6.90 °C-kg-mol. Calculate

Dmitry [639]

<u>Answer:</u> The freezing point of solution is -5.11°C

<u>Explanation:</u>

Vant hoff factor for ionic solute is the number of ions that are present in a solution. The equation for the ionization of sodium chloride follows:

$NaCl(aq.)\rightarrow Na^{+}(aq.)+Cl^-(aq.)$

The total number of ions present in the solution are 2.

To calculate the molality of solution, we use the equation:

$Molality=\frac{m_{solute}\times 1000}{M_{solute}\times W_{solvent}\text{ in grams}}$

Where,

$m_{solute}$ = Given mass of solute (NaCl) = 7.57 g

$M_{solute}$ = Molar mass of solute (NaCl) = 58.44 g/mol

$W_{solvent}$ = Mass of solvent (liquid X) = 350.0 g

Putting values in above equation, we get:

$\text{Molality of }NaCl=\frac{7.57\times 1000}{58.44\times 350.0}\\\\\text{Molality of }NaCl=0.370m$

To calculate the depression in freezing point, we use the equation:

$\Delta T=iK_fm$

where,

i = Vant hoff factor = 2

$K_f$ = molal freezing point depression constant = 6.90°C/m

m = molality of solution = 0.370 m

Putting values in above equation, we get:

$\Delta T=2\times 6.90^oC/m.g\times 0.370m\\\\\Delta T=5.11^oC$

Depression in freezing point is defined as the difference in the freezing point of water and freezing point of solution.

$\Delta T=\text{freezing point of water}-\text{freezing point of solution}$

$\Delta T$ = 5.11 °C

Freezing point of water = 0°C

Freezing point of solution = ?

Putting values in above equation, we get:

$5.106^oC=0^oC-\text{Freezing point of solution}\\\\\text{Freezing point of solution}=-5.11^oC$

Hence, the freezing point of solution is -5.11°C

7 0

4 years ago

The emission spectrum of cesium contains two lines whose frequencies are (a)

Lady bird [3.3K]

The lines are violet and blue respectively.

<h3>What is the energy?</h3>

We know that the energy of the photon could be obtained by the use of the equation;

E = hf

E = energy

h = Plank's constant

f = frequency

For the first line;

E = 6.6 * 10^-34 Js * 3.45 x 10^14 Hz = 2.3 * 10^-19 J

Given that;

E = hc/λ

λ = hc/E

λ = 6.6 * 10^-34 * 3 * 10^8/2.3 * 10^-19

λ = 8.61 * 10^-7 m or 861 nm

The color is violet

For the second line;

E = 6.6 * 10^-34 Js * 6.53 xx 10^14 Hz

E = 4.3 * 10^-19 J

E = hc/λ

λ = hc/E

λ = 6.6 * 10^-34 * 3 * 10^8/4.3 * 10^-19

λ = 4.60 * 10^- 7 m or 460 nm

The color is blue

Learn more about emission spectrum:brainly.com/question/13537021

#SPJ1

8 0

2 years ago

A student sets up a compost bin outdoors. Inside the bin microorganisms convert the student’s vegetable and paper scraps into ri

zhenek [66]

B i think thats it,.,,.,

6 0

3 years ago

Another word for oxidation is<br> Decaying<br> Rusting<br> Cutting<br> Burning

anyanavicka [17]

I believe that the answer is A. Decaying

7 0

3 years ago

Read 2 more answers