Question

28. A certain vegetable dye is pink in acidic solutions, green in neutral solutions, and blue in basic conditions. In which solution(s) will the dye be green in color? A. NaOH solution B. HCl solution C. Lemon Juice D. Salt water E. Distilled water

Answer 1

Answer 28 -

The dye will show green color in the neutral solution.

Out of all these, only distilled water is neutral.

So the dye will show green color in the distilled water.

Right option :

e) Distilled water

Answer 46-

The beta decay of Th-234 is occurred by the following reaction-

₉₀Th²³⁴$\small \rightarrow$₉₁Pa²³⁴ + _-1e⁰

(Note that in a beta decay mass number remains always same and only atomic number increases or decreases by 1 unit)

So the right option is:

B) Pa-234

Answer 47-

In an alpha decay mass number is decreased by 4 and atomic number decreases by 2

The atomic formula of uranium is - ₉₂U²³⁸

So the alpha decay of ₉₂U²³⁸ is:

₉₂U²³⁸$\small \rightarrow$₉₀Th²³⁴ + ₂$\small \alpha$⁴

So the right option is:

c) ₉₀Th²³⁴

Answer 48-

Half-life = 25.3 days

Fraction of reactant remaining after n-half lifes = (1/2)ⁿ   equation -1)

Initial concentration of P-33 = 64 gm

Final concentration of reactant = 1 gm

Fraction of reactant left = 1 / 64

Now put this value in equation 1)

1 / 64 = (1 / 2)ⁿ = 1 / 2ⁿ

By hit and trial method we can conclude that n = 6

This means that after 6 half-lifes 1 gm of P-33 is left

Now, number of days in one half-life = 25.3 days

Number of days in 6 half life = 25.3 x 6 = 151.8

Since number of days must always be a integer, we can assume number of days = 152

So we can say that after 152 days P-33 is depleted to 1gm.

Right option:

E) 152 days