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3 years ago

The largest mass extinction event in the history of the Earth occurred at the end of the _______ period.

2 answers:

7 0

The world's largest mass extinction was the Permian-Triassic event about 250 million years ago, which wiped out 95% of earth's species. It marked the end of the Paleozoic era …and the beginning of the Mesozoic.

love history [14]3 years ago

4 0

It was the Paleozoic Era about 250 million years ago

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Arrange each set in order of decreasing atomic size:

MatroZZZ [7]

Answer: The decreasing order of atomic size:

For a: Pb > Sn > Ge

For b: Sr > Sn > Te

For c: Na > F > Ne

For d: Mg > Na > Be

Explanation:

Atomic radius of an atom is defined as the total distance from the nucleus to the outermost shell of the atom.

As moving from top to bottom in a group, there is an addition of shell around the nucleus and the outermost shell gets far away from the nucleus and hence, the distance between the nucleus and outermost shell increases. Thus, increasing the atomic radii of the atom.

As moving from left to right in a period, more and more electrons get added up in the same shell and the attraction between the last electron and nucleus increases, which results in the shrinkage of size of an atom. Thus, decreasing the atomic radii of the atom on moving towards right of the periodic table.

For the given options:

Option a: Ge, Pb, Sn

Germanium (Ge) is present in Group 14 and period 4 of the periodic table.

Lead (Pb) is present in Group 14 and period 6 of the periodic table.

Tin (Sn) is present in Group 14 and period 5 of the periodic table.

So, the decreasing order of atomic size is:

Pb > Sn > Ge

Option b: Sn, Te, Sr

Tin (Sn) is present in Group 14 and period 5 of the periodic table.

Tellurium (Te) is present in Group 16 and period 5 of the periodic table.

Strontium (Sr) is present in Group 2 and period 5 of the periodic table.

So, the decreasing order of atomic size is:

Sr > Sn > Te

Option c: F, Ne, Na

Fluorine (F) is present in Group 17 and period 2 of the periodic table.

Neon (Ne) is present in Group 18 and period 2 of the periodic table.

Sodium (Na) is present in Group 1 and period 3 of the periodic table.

So, the decreasing order of atomic size is:

Na > F > Ne

Option d: Be, Mg, Na

Beryllium (Be) is present in Group 2 and period 2 of the periodic table.

Magnesium (Mg) is present in Group 2 and period 3 of the periodic table.

Sodium (Na) is present in Group 1 and period 3 of the periodic table.

So, the decreasing order of atomic size is:

Mg > Na > Be

8 0

3 years ago

La fórmula del óxido niqueloso?

murzikaleks [220]

Answer:

estoy confundido jeje

Explanation:

idek

4 0

4 years ago

Radon-222 is an alpha emitter with a half life of 3.82 days.

rewona [7]

The daughter isotope (a decay product): Polonium (Po)

<h3>Further explanation</h3>

Radioactivity is the process of unstable isotopes to stable isotopes by decay, by emitting certain particles,

alpha α particles ₂He⁴

beta β ₋₁e⁰ particles
gamma particles γ
positron particles ₁e⁰

Radon-222 emits alpha α particles ₂He⁴ , so the atomic number decreases by 2, mass number decreases by 4

Reaction

$\tt _{86}^{222}Rn\Rightarrow _{84}^{218}+_2^4He$

1. The mass number of the daughter isotope = 218

2 and 3. If we look at the periodic system, the element with atomic number 84 is Polonium (Po)

4 0

3 years ago

Why is predicting our future oil supply controversial and involves some uncertainty?

Murljashka [212]

Natural resources such as oil that are as yet undiscovered are very difficult to predict or estimate; this creates huge uncertainty and large errors in even the most rigorous scientific efforts to predict future supply. Changes in oil drilling and discovery technology can and will completely change the eventual results in the search for undiscovered resources. The controversy lies in the desire to eliminate oil from the world's energy mix in order to prevent a perceived but uncertain risk of global warming and the desire to encourage the use of alternative energy in order to reduce that risk, even though so far no alternative energy source other than natural gas, coal, and nuclear energy has been able to compete with oil economically.

3 0

4 years ago

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Which statement best describes why a machine is useful? A machine does a greater amount of work than the amount of work that is

malfutka [58]

"A machine can decrease either the input force or the input distance needed to do a given amount of work" is the best statement that describes why a machine is useful.

Answer: Option D

Explanation :

A machine is simply defined as a device that helps humans, helping them to transfer the required amount of force to compete any task, changing the direction of motion, increasing the magnitude of force to complete any task, reduce the time or distance needed to cover while performing any task.

Machines can be simple mechanical device or a combination of multiple mechanical or technical devices to reduce the amount of input force or increase the output.

8 0

3 years ago

Read 2 more answers