Half life is the time taken by a radioactive isotope to decay by half its original mass. In this case, the halflife of the radioactive isotope is 5000 years.
Initially the mass is 100 %; thus the mass that will be left will be given by;
New mass = Original mass × (1/2)^n where n is the number of half lives;
n = 10000/5000 = 2
New mass = 100% ×(1/2)^2
= 100 % × 1/4
= 25%
Therefore; the mass left after 10000 years is 25% or 1/4 of the original mass.
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Answer:
B. Particles of matter have spaces between them.
Explanation:
The particle nature model of matter is an model used to explain the properties and nature of matter. The statements of the particle nature model of matter are as follows :
1. Matter is made of small particles of atoms or molecules.
2. The particles of matter have space between them. The spaces between the particles are least in solids as they are closely packed together but are greatest in gases whose particles are far apart from each other.
3. The particles of matter are in constant motion at all times. Solids particles are not free to move due to strong molecular forces between the particles, but are constantly vibrating in their mean positions. Liquid particles free to move due to lesser molecular forces while gas molecules which have negligible intermolecular forces have the greatest ability to move.
4. The particles of matter are attracted to each other by intermolecular forces. These forces are greatest in solids and least in gases.
The correct option is B.
Answer:
8.33mol/L
Explanation:
First, let us calculate the molar mass of of formaldehyde (CH2O). This is illustrated below:
Molar Mass of CH2O = 12 + (2x1) + 16 = 12 + 2 + 16 = 30g/mol
Mass of CH2O from the question = 0.25g
Number of mole CH2O =?
Number of mole = Mass /Molar Mass
Number of mole of CH2O = 0.25/30 = 8.33x10^-3mole
Now we can calculate the molarity of formaldehyde (CH2O) as follow:
Number of mole of CH2O = 8.33x10^-3mole
Volume = 1mL
Converting 1mL to L, we have:
1000mL = 1L
Therefore 1mL = 1/1000 = 1x10^-3L
Molarity =?
Molarity = mole /Volume
Molarity = 8.33x10^-3mole/1x10^-3L
Molarity = 8.33mol/L
Therefore, the molarity of formaldehyde (CH2O) is 8.33mol/L
