Answer: b} The exact time when an individual atom will decay can be accurately predicted.
c} After each half-life, the amount of radioactive material is reduced by half.
Explanation:
All radioactive decay follows first order kinetics.
Rate law expression for first order kinetics is given by:
where,
k = rate constant
t = time taken for decay process
a = initial amount of the reactant
a - x = amount left after decay process
Expression for calculating half life, which is the time taken by the half of the reactants to decompose is:

Answer:
SeCl₆ < SeF₂ < SeO₂
Explanation:
(A) SeO₂
The central atom has 2 bond pairs and 1 lone pair. The molecule is bent shaped which has an angle of 120°.
(B) SeCl₆
The central atom has 6 bond pairs and 0 lone pair. The geometry is octahedral in which the equatorial bonds has an angle of 90° and axial bond has an angle of 90°.
(C) SeF₂
The central atom has 2 bond pairs and 2 lone pairs. The geometry is bent shape which has an angle of approximately 105.5°.
The order is:
<u>SeCl₆ < SeF₂ < SeO₂</u>