Select the correct definition of isotopes ( 2.5 points) (A) Two atoms of the same element having different number of neutrons 10 Two atoms of the same element having same atomic number but different mass number (C) Both (A) and (B) (D) None of the above.


Answer 1




(A) is correct. Isotopes are the same element that only differ in number of neutrons.

(B) is also correct. Atomic number (z) is the number of protons an atom has. Atoms of the same element will have the same number of protons.

Mass number (A) is the sum of protons and neutrons in the center. If protons between two atoms are the same but mass number is not, means they have different number of neutrons. They are isotopes.

(C) States that both A and B are correct

(D) None of the above

Option C is correct

Related Questions


How many moles of s atoms are present in 76.1 g of cs2?


76.1 gram = 1 mole of CS2

since CS2 contains 2 moles of S

the 76.1 gram of CS2 will contain the 2 mole of S atoms


Reactions that are exothermic have ΔHf values that are positive or negative


Answer : The reactions that are exothermic have values that are negative.

Explanation :

Exothermic reaction : When system releases heat energy to surrounding is known as exothermic reaction.

Endothermic reaction : When system absorbs heat energy from surrounding is known as endothermic reaction.

Enthalpy of reaction, : It is defined as the heat energy changes when the reactants go to the products.

If the heat energy is released then the reaction is exothermic and the is negative that means product is more stable than the reactant.

If the heat energy is absorbed then the reaction is endothermic and the is positive that means product is less stable than the reactant.

Hence, the reactions that are exothermic have values that are negative.

The enthalpy change of an exothermic reaction has a negative value.

The balanced chemical equation for the reaction of copper (Cu) and silver nitrate (AgNO3) is shown below. Cu + 2AgNO3 2Ag + Cu(NO3)2 How many moles of copper must react to form 0.854 mol Ag?


The moles of copper that must react to form 0.854 mol Ag is 1.75 mol. The correct option is B.

What is molar mass?

A substance's molar mass is the mass in grams of one mole of the substance. The molar mass of a substance can be calculated by adding the molar masses of its constituent atoms.

The calculated molar mass can then be used to convert between mass and the number of moles of the substance.

A mole of a compound contains the number of molecules (molecular compound) or formula units calculated by Avogadro.

Cu + 2 AgNO₃ =  2 Ag + Cu(NO₃)₂

Let the moles of copper is x, so the mole ratio:

1 mole Cu = 2 moles Ag

x mole Cu = 3.50 moles Ag

moles Cu = 3.50 x 1 / 2

moles Cu = 3.50 / 2

moles Cu = 1.75 moles

Thus, the correct option is B.

For more details regarding molar mass, visit:


Your question seems incomplete, the missing options are:

0.175 mol

1.75 mol

7.00 mol

17.0 mol

1 mol Cu - 2 mol Ag
x             - 0.854 mol Ag


0.427 mol Cu

Will a larger solute particle take a longer or a shorter amount of time to dissolve than a smaller particle? A) Always shorter

B) Always longer

C) Shorter at low temperatures, but longer at high temperatures

D) Always the same amount of time


The answer is B.Always Longer I hope this helps you 

According to KMT, at constant pressure and temperature, the frequency and force of molecule-wall collisions are constant. So increasing the number of gaseous molecules will require a proportional increase in the container volume in order to yield a decrease in the number of collisions per unit area to make up for the increased frequency of collisions. What gas law is KMT explaining?



Boyle´s Law


If we increase the volume of a gas, its pressure will decrease that is why in this question the pressure was decreased to  yield the decrease in the number of collisions.

This is Boyle´s law which states that the pressure of a gas is inversely proportional to the volume of its container.

It is expressed mathematically  as P₁V₁ = P₂V₂

where the subscripts refer to intial and final conditions.


When 18.5 g of HgO(s) is decomposed to form Hg(l) and O2(g), 7.75 kJ of heat is absorbed at standard-state conditions. What is the standard enthalpy of formation (ΔH°f) of HgO(s)? –90.7 kJ/mol



The standard enthalpy of formation of HgO is -90.7 kJ/mol.


The reaction between Hg and oxygen is as follows.

From the given,

Molar mass of HgO = 216.59 g/mol

Mass of HgO decomposed = 18.5 g

Amount of heat absorbed = 7.75 kJ

From the reaction,

The standard  enthalpy of formation =

During the decomposition of 1 mol of HgO , 90.7 kJ of energy absorbed.

For the formation of 1 mol of HgO , 90.7 kJ of energy is release

Therefore, the enthalpy of formation of mercury(II)Oxide is -90.7 kJ/mol


How does predation affect an ecosystem?


Well if the predator population get to be too big, then the prey population will drastically decrease which will chase problems, like extinction.


Predator-prey relationships are something we find in every ecosystem. Predators are organisms that kill and eat other organisms for food resources. Prey, on the other hand, are organisms that are killed and eaten by other organisms. This process of one organism feeding on another is commonly referred to as predation.

In ecosystems, balance is key, especially between organisms. To maintain this balance, predator and prey populations follow a predictable cycle. Predators help to control the prey population, while prey give predators the nutrients and energy needed to survive. In other words—eat, or be eaten.



On the Fahrenheit scale at what temperature does water boil at?


212 degrees Fahrenheit is the temperature at which water boils.

Water boils at 212 for fahenheit to be exact and 100 for celcius


In a closed container with a fixed volume, when the temperature of a gas doubles, the pressure of the gas is? A)Reduced by half.
C)increased by half.
D)left changed.



The pressure of the gas is:



Byole's Law  = Pressure of fixed amount of gas is inversely proportional to Volume at constant temperature.

PV = k = constant

P1V1 = P2V2

Charle's Law: The volume of ideal gas at fixed pressure is directly proportional to Pressure.

V/T = constant

V1/T1 = V2/T2

On combinig the charles and byole's law , we get:

Now , According to question :

V2 = V1

T2 = 2(T1)

We have to find the relation between the pressure :

insert the value in the equation

V1 and V1 & T1 and T1 cancels each other,

So we get

P2 = 2 P1

So the new pressure is double of the original pressure

Random Questions