Question

Which element out of the elements with

atomic nos. 25, 48, 82 & 87 will lie in the

s-block of the modern

periodic table.

(A) 25(B) 48(C) 82(D) 87....................... Pls help somone ​

Answer 1

Explanation:

B is the right sahi hai lekin

Answer 2

Method-1

Study the atomic numbers of all the noble gases. This will help you a lot in many problems.

The atomic numbers are:

1. 2 -He
2. 10 - Ne
3. 18 - Ar
4. 36- Kr
5. 54 - Xe
6. 86 - Rn
7. 118 - Og

The atomic number of an element in s block will be one or two more than the atomic number of the noble gas. (As s block has two groups)

Here, out of all options, atomic number 87 is one more than 86, which is Radon. So, it belongs to group 1 alkali metals (Fr)

(If you want to consider this method for  p block, understand that an element would be considered to be in p block if its atomic number falls from Z-1 to Z-6 as there are 6 groups in p block)

Method -2

In an group the atomic numbers will be ordered in the following pattern:

8,8,18,18,32

This means, adding 8 to the atomic number of the first element of the group (except d and f) will give the atomic number of the second. Adding 18 will give the third, adding 18 to third will give fourth...etc

e.g. considering alkali metals,

1. Li -3
2. Na - 11 (3+8)
3. K- 19 ( 11 + 8)
4. Rb - 37 (19 + 18)
5. Cs - 55 ( 37 + 18)
6. Fr - 87 ( 55 + 32)