Question

The radius of which of the following orbit is same as that of the first bhor's orbit of hydrogen atom? a (he+) b(li2+) c (li2+) D (Be3+)

Answer 1

1) n=2, Li2+ 

2) n=2, Be3+ 

3) n=2, He+ 

4) n=3, Li2+

Logic:

Radius of Bohr's orbit in hydrogen and hydrogen like species can be calculated by using the following formula.



Where 

n = prinicipal quantum number of orbit.

Z = atomic number

Now compare the n2/Z values of orbits for given species with that of hydrogen's first orbit to get the answer.

Solution:

 1st orbit of H atomOption 1
n=2, Li2+ Option 2
n=2, Be3+Option 3
n=2, He+Option 4
n=3, Li2+n =12223Z = 13423n2/Z  12/1 = 122/3 = 4/322/4 = 122/2 = 232/3 = 3

Conclusion:

Since the n2/Z values are same for second orbit of Be3+ and first orbit of H, their radii are also equal. Answer is option 2.

Answer 2

Answer:

Answer is b

Explanation:

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