1.Which statement best describes an oxidation-reduction reaction?(1 point) A. a chemical reaction in which there are fewer products than reactants

B. a chemical reaction that involves oxygen

C. a chemical reaction in which electrons are released from the system

D. a chemical reaction in which electrons are transferred between reactants

2.Beryllium (Be) has four electrons. Fluorine (F) has nine electrons. Which chemical formula shows the correct subscripts for the product of the reaction when beryllium and fluorine combine?(1 point)

A. Be2F

B. BeF

C. Be2F2

D. BeF2

Use the reaction to answer the question.

2KCl → 2K + Cl2

Which type of reaction is shown?

(1 point)

A. combination

B. displacement

C. decomposition

D. combustion

D

Explanation:

part 1: the half-life of the element is 22 years.

part 2: it will take 132.02 year for the sample to decay from 308.0 g to 4.8125 g.

explanation:

part 1: there are two ways to determine the half life time.

first way: the half life time can be determined directly from its definition as it is the time required for the sample to decay to its half concentration.

from the data the initial concentration was 45.0 g and decayed to its half value (22.5 g) in 22.0 years.

second way: the radio active decay is considered first order reaction so we can use the laws of first order reactions.

k = (1/t) ln (a/a-x), where k is the rate constant of the reaction,

t is the time of the reaction

a is the initial concentration of the reactant

a-x is the remaining concentration at time (t)

a = 45.0 g the initial concentration at t = 0 year.

at t = 22 year, a-x = 22.5 g

then k = (1/22 year) ln (45.0 g/ 22.5 g) = 0.0315 year-1.

the half-life time (t1/2) = ln 2/ k = 0.693/ k =0.693/ 0.0315 = 22 years.

part 2:

using the same law k = (1/t) ln (a/a-x),

using the given data; a = 308.0 g and a-x = 4.8125 g and the calculated k from the part 1 (k = 0.0315 year-1)

t = (1/k) ln (a/a-x) = (1/0.0315) ln (308.0/ 4.8125) = 132.02 years

the answer is d. 74.02