1. What fraction of a sample of N-16 remains undecayed after 42.78 seconds?

1/64

Explanation:

From the question given above, the following data were obtained:

Time (t) = 42.78 s

Fraction of N–16 remaining (N/N₀) =?

NOTE:

N₀ => is the original amount.

N => is the amount remaining.

Next, we shall determine the number of half-lives that has elapsed. This can be obtained as follow:

Time (t) = 42.78 s

Half-life (t½) of N–16 = 7.1 s

Number of half-lives (n) =?

n = t / t½

n = 42.78 / 7.1

n = 6

Thus, 6 half-lives has elapsed.

Finally, we shall determine the fraction of N–16 that remains undecayed. This can be obtained as follow:

Number of half-lives (n) = 6

Fraction of N–16 remaining (N/N₀) =?

N = 1/2ⁿ × N₀

N = 1/2⁶ × N₀

N = 1/64 × N₀

Divide both side by N₀

N/N₀ = 1/64

Therefore, 1/64 of the sample remains undecayed.

the only liquid elements at standard temperature and pressure are bromine (br) and mercury (hg). although, elements caesium (cs), rubidium (rb), francium (fr) and gallium (ga) become liquid at or just above room temperature.

explanation:

1.solid

2.carbon dioxide

3.helium