1-The atomic number of an element

A. the whole number nearest to its mass

B. the number of protons in its nucleus

C. the nearest whole number of hydrogen atoms having the same mass as a single atom of the given element

D. the number of neutrons in its nucleus

E. its order of discovery

2 -The isotopes of an element

A. cannot be separated at all

B. occur well separated in nature

C. has similar chemical behavior

D. cannot be separated by physical methods

E. have equal masses

3 - The half-life of a radioactive substance is

A. half the time it takes for the entire substance to decay

B. usually about 50 years

C. the time for radium to change into lead

D. calculated from E = mc2

E. the time for half the substance to decay

4 -The relation between the disintegration constant λ and the half -life T of a radioactive substance is:

A. λ =2T

B. λ =1/T

C. λ =2/T

D.λT =ln2

E. λT = ln(1/2)

5. Possible units for the disintegration constant λ are

A. depends on the initial number of A atoms

B. depends on the initial number of B atoms

C. is an exponentially increasing function of time

D. is an exponentially decreasing function of time