Chemistry

NEET Class 12

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The emission spectrum of hydrogen discovered first and the region of the electromagnetic spectrum in which it belongs, respectively are

Lyman, ultraviolet

Lyman, visible

Balmer, ultraviolet

Balmer, visible

D.

Balmer, visible

Balmer explained the wave numbers of spectral lines present in the visible region in hydrogen spectrum. These are given by-

$\overline{)\mathrm{v}}$ (cm^{-1}) = 109677 $\left(\frac{1}{{\left(2\right)}^{2}}-\frac{1}{{\mathrm{n}}^{2}}\right)$

Here, n = 3, 4, 5, ....

Thus, Balmer spectrum of hydrogen was discovered first and it lies in the visible region.

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2.

As per de-Broglie's formula a macroscopic particle of mass 100 g and moving at a velocity of 100 cm s^{-1} will have a wavelength of

6.6 × 10

^{-29}cm6.6 × 10

^{-30}cm6.6 × 10

^{-31}cm6.6 × 10

^{-32}cm

3.

For one mole of an ideal gas,the slope of V *vs* T curve at constant pressure of 2 atm is X L mol^{-1} K^{-1}.The value of the ideal universal gas constant 'R' in terms of X is

X L atm mol

^{-1}K^{-1}$\frac{\mathrm{X}}{2}$L atm mol

^{-1}K^{-1}2X L atm mol

^{-1}K^{-1}2 X atm L

^{-1}mol^{-1}K^{-1}

4.

At a certain temperature the time required for the complete diffusion of 200-mL of H_{2} gas is 30 min. The time required for the complete diffusion of 50 mL of O_{2} gas at the same temperature will be

60 min

30 min

45 min

15 min

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5.

The correct order of decreasing H-C-H angle in the following molecule is

I > II > III

II > I > III

III > II > I

I > III > II

6.

During the emission of a positron from a nucleus, the mass number of the daughter element remains the same but the atomic number

is decreased by 1 unit

is decreased by 2 units·

is increased by 1 unit

remains unchanged

7.

β- emission is always accompained by

formation of antineutrino and α-particle

emission of α-particle and γ-ray

formation of antineutrino and γ-ray

formation of antineutrino and positron

8.

Four gases P, Q, R and S have almost same values of 'b' but their 'a' values (a, b are van der Waals' constants) are in the order Q < R < S < P. At a particular temperature, among the four gases, the most easily liquefiable one is

P

Q

R

S

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10.

The correct order of decreasing length of the bond as indicated by the arrow in the following structures is

I > II > III

II > I > III

III > II > I

I > III > II

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