<h3>Answer:</h3>
18.75 grams
<h3>Explanation:</h3>
- Half-life refers to the time taken by a radioactive material to decay by half of the original mass.
- In this case, the half-life of element X is 10 years, which means it takes 10 years for a given mass of the element to decay by half of its original mass.
- To calculate the amount that remained after decay we use;
Remaining mass = Original mass × (1/2)^n, where n is the number of half-lives
Number of half-lives = Time for the decay ÷ Half-life
= 40 years ÷ 10 years
= 4
Therefore;
Remaining mass = 300 g × (1/2)⁴
= 300 g × 1/16
= 18.75 g
Hence, a mass of 300 g of an element X decays to 18.75 g after 40 years.
Answer:
b. source
Explanation:
The source is where something comes from. i.e. The source of sunlight is the sun.
<u>Answer:</u> The salinity of ocean water is 34 ppt.
<u>Explanation:</u>
Salinity is defined as the number of grams of salts present per kilogram of seawater. It is expressed in parts per thousand.
The formula used to calculate the salinity of ocean water or sea water is:
We are given:
Mass of salts = 17 g
Mass of sea water = 500 g
Putting values in above equation, we get:
Hence, the salinity of ocean water is 34 ppt.
Answer:
The three main atomic particles are protons, neutrons and electrons. The atomic number of an atom identifies the number of protons in the atom. This is the defining characteristic of an element. An atom can gain or lose neutrons or electrons while retaining its elemental identity.
Explanation:
Answer:
2.41x10²¹ atoms
Explanation:
First we <u>calculate the mass of nickel in the coin</u>, using <em>the given mass and percent composition</em>:
- 0.942 g * 25/100 = 0.2355 g Ni
Then we<u> convert 0.2355 grams of nickel to moles</u>, using its<em> molar mass</em>:
- 0.2355 g Ni ÷ 58.69 g/mol = 0.004 mol
Finally we <u>convert moles into number of atoms</u>, using <em>Avogadro's number</em>:
- 0.004 mol * 6.023x10²³ atoms/mol = 2.41x10²¹ atoms
