PLS PLS PLS HELP I WILL MARK YOU BRAINLYEST PLS

Answer:

25 atoms

Explanation:

Given data:

Total number of atoms = 400 atom

Atoms remain after 4 half lives passed = ?

Solution:

At time zero = 400 atom

At first half life = 400 atom/2 = 200 atom

At 2nd half life = 200 atom/2 = 100 atom

At 3rd half life = 100 atom/2 = 50 atom

At 4th half life = 50 atom/2 = 25 atom

Thus, 25 atoms are remained after 4 half lives.

25 atoms of the radioactive atoms will remain after 4 half lives.

    Given in the question,

Expression for the amount remaining of a radioactive element after 'n' half lives is given by,

[tex]N=N_0(\frac{1}{2})^n[/tex]

Here, [tex]N_0=[/tex] Initial amount

[tex]n=[/tex] Number of half lives

By substituting the vales of [tex]N_0[/tex] and [tex]n[/tex] in the question,

[tex]N=400(\frac{1}{2})^4[/tex]

   [tex]=\frac{400}{16}[/tex]

   [tex]=25[/tex]

        Therefore, 25 atoms of the radioactive atoms will remain after 4 half lives.

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Answer:

6

Explanation:

Answer:

A

Explanation:

A hydroxide ion is given as:

       OH⁻

The electron dot notation shows only the chemical symbol of the element surrounded by dots to represent the valence electrons. The chemical symbol denotes the nucleus and all electrons except the valence electrons.

The dots are arranged on the four sides in pairs.

Oxygen is made up of 6 valence electrons, and since the ion has a net negative charge, the hydrogen and oxygen achieved their stable configuration this way.

Answer:

See the answer below

Explanation:

The speed of light in air and space is faster than the speed of sound in the same media. Light travels with a speed of approximately 3 x [tex]10^8[/tex] m/s while sound can only travel at 343 m/s (at 20 [tex]^oC[/tex]).

Consequently, the visuals of a batter striking a pitched ball which travel by light and is perceived through the eyes would be seen before the sound of the strike.

The difference in the speeds of light and that of sound largely explains the difference in the communication received about seeing a batter striking a pitched ball before hearing the sound of the strike

Answer:

It would be the third answer.

Explanation:

This is because over the next few minutes, the heat would radiate away from the atoms in the metal plate and the atoms around the plate would absorb this radiation.

Answer:

10 km/hr

............

The speed of a bicycle is 10 km/hour or 0.27 m/sec.

The speed may be defined as the rate of change of position of an object in any direction. It is significantly measured as the ratio of distance to the time in which the distance was covered.  Speed is a type of scalar quantity that has only direction but no magnitude.

According to the question, the distance traveled by bicycle = 20 km or 2000 meters.

The total time is taken = 2 hours or 7200 seconds.  

Now, the formula for calculating the speed is as follows:

S = Distance/ Time = 20km/2 hours = 10 km/hour.

S = Distance/ Time = 2000 meters/7200 seconds = 0.277 m/sec.

Therefore, the speed of a bicycle is 10 km/hour or 0.27 m/sec.

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Answer:

A

Explanation:

A conversion factor is used to change the units of a measured quantity without changing its value.

Unit conversion is very important because the rest of the world other than three contries uses the metric system. So, converting unitsis important in science because it uses the metric system. The metric system are measurements like cm, m, l, mL, etc.

Answer:

D

Explanation:

Answer: When I see you again!

Explanation:

Answer:

Percient yield of reaction: 85 %

Explanation:

The reaction is:

PCl₃ + 3H₂O → H₃PO₃ + 3HCl

We only have data from the chloride, so we assume water is in excess. We convert the mass to moles:

62 g . 1mol / 137.32 g = 0.452 mol

If ratio is 1:3, from 0.452 mol we would produce three times as big, that amount. (0.452 . 3) = 1.36 moles of HCl.

We convert the amount to mass.

1.36 mol . 36.45g / 1mol = 49.4 g

This value of produced HCl is the theoretical yield. To determine the percent yield we make:

(Yield produced / Theoretical yield) . 100

(42 g / 49.4g) . 100 = 85%

Answer:

Yes it is 85.0%

Explanation:

Answer:

answer in the picture hi shirllleeyyyyy

Answer: theres 5

Explanation: valence electrons are the electrons in the outer shell. I took that test a few weeks ago :0

Answer:

i have no idea and i dont get it

Answer:

nut

Explanation:

(I) [tex]H_2SO_4+ 2NaHCO_3--> Na_2SO_4 + 2 H_2O + 2CO_2[/tex]

(II) [tex]H_2+I_2 --> 2HI[/tex]

(III) [tex]2NaOH+H_2SO_4--> Na_2SO_4+ 2H_2O[/tex]

(IV) [tex]2FeSO_4--> Fe_2O_3+SO_2+SO_3[/tex]

(V) [tex]2C_3H_6O_2+7O_2-->6CO_2+6H_2O[/tex]

------------------------------------------------------------------------------------------------------------

(I) [tex]H_2SO_4[/tex]

(ANS) [tex]98 \frac{grams}{mol}[/tex]

__________________________________________________________

Solution:

Molecular mass of,

H = 1

S = 32

O = 16

Now,

There are 2 atoms of Hydrogen, 1 atoms of Sulfur and 4 atoms of Oxygen present, thus,

[tex]H_2SO_4 = (1x2)+32+(16x4)[/tex]

[tex]H_2SO_4 = 98 \frac{grams}{mol}[/tex]

(II) [tex]CH_4[/tex]

(ANS) [tex]16 \frac{gram}{mol}[/tex]

_________________________________________________________

Solution:

Molecular Mass,

Carbon = 12

Hydrogen = 1

Now

There are 1 atom of Oxygen and 4 atoms of Hydrogen present, thus,

[tex]CH_4 = 12 + (1x4)[/tex]

[tex]CH_4 = 16\frac{grams}{mol}[/tex]

(III) [tex]NH_3[/tex]

(ANS) [tex]17 \frac{grams}{mol}[/tex]

__________________________________________________________

Solution:

Molecular Mass,

Nitrogen = 14 grams

Hydrogen = 1

Now,

There are 1 atoms of Nitrogen and 3 atoms of Hydrogen present, thus,

[tex]NH_3 = 14 + (1x3)[/tex]

[tex]NH_3 = 17 \frac{grams}{mol}[/tex]

56     71

x       35.5

[tex]X = \frac{56 x 35.5}{71}[/tex]

Simplify the equation

X = 28 grams

__________________________________________________________

Answer:

28 grams of Iron(fe) will react with chlorine.

Answer:

1. A

Explanation:

1.A True we can identify solutions based on the color of the solutions. If you look at our  universal PH color chart. Red, Orange, and yellow are acids.

2. D, If you look at the pH levels. Both B and C have a pH level equal to or greater than 7. Note that any pH level 7 or higher is a basic solution.

3.A

Looking at the pH level we can see that this is an acidic solution. So, by adding more water. The acidity will lessen.

Answer:

It blocks pathogens from getting inside our body.

Explanation:

The skin is the biggest organ, it cover the whole body and organ system from any toxic things.

Answer:

The volume is  [tex]V_2 =15.33 \ L[/tex]

Explanation:

From the question we are told that

    The number of moles of the gas is  [tex]n_1 = 2.10 \ moles[/tex]

      The volume of the gas is  [tex]V = 46.0 \ L[/tex]

        The  of moles of the gas that leaked is  [tex]n_2 = 0.700 \ mol[/tex]

Generally from the ideal gas law

      [tex]PV = nRT[/tex]        

Generally at constant pressure and temperature

        [tex]\frac{V}{n} = constant[/tex]

So   [tex]\frac{V_1 }{n_1} = \frac{V_2 }{n_2}[/tex]

=>    [tex]V_2 = \frac{ V_1 * n_2 }{ n_1}[/tex]

=>    [tex]V_2 = \frac{ 46.0 * 0.700 }{ 2.10 }[/tex]  

=>    [tex]V_2 =15.33 \ L[/tex]

Answer:

2

Explanation:

If you take H and N, that is two molecules right off the bat.  If you take O4, that makes 6.  Take the total of all 6, and multiply it by 3, with equals 18.  

3HNO4 = 18

Answer: They are non-reactive and don't conform with other elements to form compounds. Because they are non-reactive, they don't corrode easily.

Explanation:

The  properties of gold and platinum  which make these metals desirable for jewelry is due to their electronic configuration due to which they are non-reactive and do not corrode easily.

Electronic configuration is defined as the distribution of electrons which are present in an atom or molecule in atomic or molecular orbitals.It describes how each electron moves independently in an orbital.

Knowledge of electronic configuration is necessary for understanding the structure of periodic table.It helps in understanding the chemical properties of elements.

Elements undergo chemical reactions in order to achieve stability. Main group elements obey the octet rule in their electronic configuration while the transition elements follow the 18 electron rule. Noble elements have valence shell complete in ground state and hence are said to be stable.

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Answer:

B. Plant cells have a cell wall and chloroplasts; animal cells do not have either of these structures.

Explanation:

A major difference between a plant cell and an animal cell is presence of chloroplasts in plant cells. Another key difference between plant and animal cells is the presence of a cell wall in plant cells. Both structures are absent in an animal cells.

The cell wall surrounds the plasma membrane of plant cells. This helps to provide the required tensile strength and protection against mechanical and osmotic stress.

Cell walls also help plants to maintain shape and rigidity.

The plant cell has a cell wall and chloroplast, while the animal cell lacks both of them. Thus, option B is correct.

The cell has been the smallest unit of life that has been performing varying functions with the help of different organelles.

The plant cell has been exposed to harsh environmental conditions, thus has been consisting of the cell wall along with the cell membrane. However, animal cell lacks a cell wall.

The food has been processed in the plant cells with the help of photosynthesis that required chlorophyll. The chlorophyll has been consisted in the chloroplast. Thus plants cell have consisted of chloroplast, however, animal cells lack chlorophyll as well as chloroplasts.

Thus, the plant cell has a cell wall and chloroplast, while the animal cell lacks both of them. Thus, option B is correct.

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Answer:

eight valence electrons

Answer:

it has 8 valence electrons

Answer:

This question is incomplete but the correct option is B

Explanation:

This question is incomplete because of the absence of the "Reference Table S", however the question can still be answered in the absence of the table. The energy described in the question is the ionization energy (energy required to remove the most loosely bound electron in an atom). This question seeks to know the atom (from the options provided) with the least ionization energy.

Ionization energy increases from left to right across the period because it's easier to remove a single electron (valence electron) from the outermost shell than to remove two electrons from the same shell; thus the more the valence electrons (in a shell), the higher the ionization energy. Thus, bromine (Br) and tin (Sn) have high ionization energies because they have more number of electrons in there outermost shell.

Berylium (Be) and strontium (Sr) are both in the group 2 of the periodic table because they both have 2 electrons in there outermost shell. Ionization energy decreases down a group. This is because the farther an electron is from the nucleus, the weaker the force of attraction between the nucleus and the electron. Thus, strontium (Sr) would have a lesser ionization energy between the two and would indeed have the least ionization among the options provided. Hence, the correct option is B

Answer:

The atomic number is the number of protons in the nucleus of an atom . The number of protons define the identity of an element

Answer:

D

Explanation:

Answer:Naming Covalent compounds

A B

hexaboron silicide B6Si

chlorine dioxide ClO2

hydrogen iodide HI

iodine pentafluoride IF5

Explanation: