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Structure of Atom

NEET Chemistry · 92 questions · Page 10 of 10 · Click an option or "Show Solution" to reveal answer

Q91
Radius of the first excited state of Helium ion is given as : a0→\mathrm{a}_0 \rightarrow radius of first stationary state of hydrogen atom.
A r=a04\mathrm{r}=\dfrac{\mathrm{a}_0}{4}
B r=2a0\mathrm{r}=2 \mathrm{a}_0
C r=4a0\mathrm{r}=4 \mathrm{a}_0
D r=a02\mathrm{r=\dfrac{a_0}{2}}
Correct Answer
Option B
Solution
rn=n2 a0Zr_n = \frac{n^2\, a_0}{Z}

For the helium ion, which is hydrogen-like with a nuclear charge of

Z=2Z = 2

, the first excited state corresponds to

n=2n = 2

. Substituting these values:

r2=(2)2 a02=4 a02=2 a0r_2 = \frac{(2)^2\, a_0}{2} = \frac{4\, a_0}{2} = 2\, a_0

Thus, the radius of the first excited state of the helium ion is

2 a02\, a_0

.

Q92
Of the following sets which one does NOT contain isoelectronic species?
A BO33−BO_3^{3 - }, CO32−CO_3^{2 - }, NO3−NO_3^{- }
B SO32−SO_3^{2 - }, CO32−CO_3^{2 - }, NO3−NO_3^{-}
C CN−CN^{- }, N2N_2, C22−C_2^{2 - }
D PO43−PO_4^{3 - }, SO42−SO_4^{2 - }, ClO4−ClO_4^{ - }
Correct Answer
Option B
Solution

In

SO32−SO_3^{2 - }

no of electrons = 16 + 24 + 2 = 42 In

CO32−CO_3^{2 - }

no of electrons = 6 + 24 + 2 = 32 In

NO3−NO_3^{-}

no of electrons = 7 + 24 + 1 = 32 So they are not isoelectronic.

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