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kykrilka [37]
3 years ago
7

Help please all please

Chemistry
2 answers:
Luden [163]3 years ago
5 0

Answer:

I don’t want to download a pdf that I don’t know what it is…

Also, brainly strictly says that we can’t post questions about a test or quiz that is found in school…

Explanation:

Lilit [14]3 years ago
3 0

Answer:

wnich subject and which class pdf i will help you tell me

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What existed during the mesozoic era
Ilia_Sergeevich [38]
Mezoic era began 252m years ago and ended 6.6m years ago.
It was a time of geological and biological transition. During this era the continents began to drift to their present configuration.
3 of the largest mass extinction occurred at this era. One which include the dinosaurs.
I hope this helped. :)
3 0
3 years ago
Radioactive decay can be described by the following equation where is the original amount of the substance, is the amount of the
soldi70 [24.7K]

Answer:

Iron remains = 17.49 mg

Explanation:

Half life of iron -55 = 2.737 years (Source)

t_{1/2}=\frac {ln\ 2}{k}

Where, k is rate constant

So,  

k=\frac {ln\ 2}{t_{1/2}}

k=\frac {ln\ 2}{2.737}\ year^{-1}

The rate constant, k = 0.2533 year⁻¹

Time = 2.41 years

[A_0] = 32.2 mg

Using integrated rate law for first order kinetics as:

[A_t]=[A_0]e^{-kt}

Where,  

[A_t] is the concentration at time t

[A_0] is the initial concentration

So,  

[A_t]=32.2\times e^{-0.2533\times 2.41}\ mg

[A_t]=32.2\times e^{-0.610453}\ mg

[A_t]=17.49\ mg

<u>Iron remains = 17.49 mg</u>

8 0
3 years ago
A chemist takes 50-gram sample of sulfur powder that has a melting point of 115.2 °C. What is the melting point of a 100-gram sa
Viktor [21]

Answer:

115.2 °C since melting point is an intensive property  

Step-by-step explanation:

The melting point of a substance does not depend on how much you have.

For example, the melting point of water is 0 °C, whether it is an ice cube from the refrigerator or in the frozen pond outside.

The freezing point of a substance is an <em>intensive property</em>.

Thus, the melting point of 100 g of sulfur is 115.2 °C because melting point in an intensive property.

7 0
3 years ago
From 1962 until 1981 pennies were made from 95% copper and 5% zinc and had a mass of 3.1 g. Starting in 1982, pennies have been
Sloan [31]

Answer:

2.7724 g

Explanation:

Mass of pre- 1892 pennies = 3.1 g

Abundance = 45.4 %

Mass of post 1892 pennies = 2.5 g

Abundance = 100 - 45.4 = 54.6 %

The average mass is given as = ( 3.1 g   *  45.4 / 100)  +  (2.5g  *  54.6 / 100)

Average Mass = 3.1 * 0.454   +   2.5  *  0.546

Average Mass = 1.4074  + 1.365 = 2.7724 g

8 0
3 years ago
The universe cooled after the Big Bang. At some point, hydrogen atoms combined to form helium. What is this process called?
LiRa [457]
This process is called as Nuclear Fusion
4 0
3 years ago
Read 2 more answers
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