3.
a rock sample contains 80g of a potassium-40
(k10) isotope with a half-life of 1.25 billion years.
how much of the potassium-40 isotope will remain
after 2.5 billion years have passed?
a. og
b. 10g
c. 20g
d. 80g

20 g

We are given;

Original mass of K-40 before decay = 80 g

Half life of Potassium-40 = 1.25 billion years

Time taken by the decay = 2.5 billion years

We are required to calculate the mass of K-10 that will remain after 2.5 billion years.

Using the formula;

Remaining mass = Original mass × (1/2)^n

where n is the number of half lives

Number of half lives, n = Time taken ÷ half-life

                                     = 2.5 billion years ÷ 1.25 billion years

                                     = 2

Remaining mass = 80 g × (0.5)^2

                            = 80 g × 0.25      

                            = 20 g

Therefore, the mass of K-40 isotope that will remain after 2.5 billion years is 20 g.

answer: option (b) is the correct answer.

explanation:

a covalent bond is formed by sharing of electrons. whereas polarity arises due to difference in electronegativity of two atoms.

therefore, more is the electronegativity of an atom which combines with the titanium, more readily it will induce a partial positive and negative charge.

thus, out of the given options fluorine is most electronegative and has an incomplete octet. therefore, it will readily combine with titanium to share the electrons and complete its octet.  

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