36. Given the following half-lives, which of the isotopes is the most stable? A)

Question

36.

Given the following half-lives, which of the isotopes is the most stable?

A) 56 s
B) 72 s
C) 0.92 min
D) 0.015 hr

37.

A) 10.0 g
B) 2.5 g
C) 6.67 g
D) 5.0 g

38.

Isotopes have __________.

A) the same number of neutrons but a different number of protons
B) different numbers of protons and neutrons
C) the same number protons and the same number of neutrons
D) the same number of protons but a different number of neutrons

39.

A) gamma emission
B) beta emission
C) alpha emission
D) neutron emission

40.

A) 17,400
B) 23,200
C) 11,600
D) 5800

Explanation / Answer

1. More the half life, lesser the rate constant and more stable is the isotope.

2. from M= Mo*e(-kt), K= rate constant =0.693/ half life= 0.693/5=0.1386/hr

M0= initial mass =20gm, M = mass at any time, t , M= 20*e(-0.1386*15) = 2.5 gm

3. Isotopes of the same elements will have same number of protons but different number of neutrons (D is correct)

4. Alpha particle is same as Helium nucleus. Hence alpha particle is emitted

5. Ct =Co* e(-kt)

Ct/CO= 0.5 =e(-kt)

ln(0.5)= -kt

t= 0.693/K but K= 0.693/5730

t= 5730 years ( D is close to the answer)

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