Question

a. How many neutrons are in $K-41$?

b. Write the electron arrangement for potassium.

c. Which is the larger atom. $K$or $Cs$?

d. Which is the smallest atom, $K,As,$or $Br$?

e. If John's potato field has an area of $34.5$hectares. How many pounds of fertilizer does John need to use?

Short answer

(a) The no. of neutrons are $22$

(b) The electron arrangement for potassium is $\left[Ar\right]4s^1$

(c) The larger atom is$Cs$

(d) The smallest atom is $Br$

(e) Amount of fertilizer John needs to use is$12930.1lb$

Step-by-step solution

Part (a) Step 1: Given information 

We need to find the no. of neutrons in$K-41$

Part (a) Step 2: Simplify

We know that,

Mass no. is equal to the sum of no. of protons and no. of neutrons.

And Atomic no. of potassium is $19$

Also, Atomic no. is equal to no. of protons. Hence no. of protons are, $19$

Here, mass no. is $41$

Therefore,

No. of neutrons are equal to the difference of mass no. and no. of protons i.e.$41-19=22$

Part (b) Step 1: Given information

We need to find the electron arrangement for potassium

Part (b) Step 2: Explanation

We know that,

Atomic no. of potassium is $19$

And atomic no. is equal to no. of electrons

Hence no. of electrons are $19$

Therefore electron arrangement of potassium is,

$\left[Ar\right]4s^1$

Where$Ar$is argon having atomic no.$18$

Part (c) Step 1: Given information

We need to find the larger atom among$K,Cs$

Part (c) Step 2: Explanation

We know that,

$K$and $Cs$lie in the same group but different periods.

And as we move top to bottom in a group atomic size increases

Since, $K$is at the top as compared to $Cs$

Therefore, The larger atom is $Cs$

Part (d) Step 1: Given information

We need to find the smallest atom among$K,As,Br$

Part (d) Step 2: Explanation

We know that,

$K,As,Br$lie in the same period but in different groups.

And Size of the atom decreases as we move left to right in the period.

Since $Br$is in the right as compared to both the other atoms

Therefore, The smallest atom is $Br$

Part (e) Step 1: Given information

We are given that area of John's potato field is$34.5$hectares.

Part (e) Step 2: Simplify

We know that,

John needs to apply $170kg$fertilizer per hectare.

As the field is $34.5$hectares

Therefore, fertilizer needed is,

$$\begin{gathered} 34.5\times 170 \\ =5865kg \\ =5865\times 2.2lb \\ =12930.1lb \end{gathered}$$