What is the area beyond the black hole where the black hole has stopped expanding and matter will no longer be pulled in?

The half-life of radioactive substance is 2.5 minutes. what fraction of the origional radioactive remains after 10 mins

saul85 [17]

The answer is 1/16.

Half-life is the time required for the amount of a sample to half its value.
To calculate this, we will use the following formulas:
1. $(1/2)^{n} = x$ ,
where:
n - a number of half-lives
x - a remained fraction of a sample

2. $t_{1/2} = \frac{t}{n}$
where:
 $t_{1/2}$ - half-life
t - total time elapsed
n - a number of half-lives

So, we know:
t = 10 min
 $t_{1/2}$ = 2.5 min

We need:
n = ?
x = ?

We could first use the second equation to calculate n:
If:
$t_{1/2} = \frac{t}{n}$ ,
Then:
$n = \frac{t}{ t_{1/2} }$
⇒ $n = \frac{10 min}{2.5 min}$
⇒ $n=4$ 

Now we can use the first equation to calculate the remained fraction of the sample.
 $(1/2)^{n} = x$
⇒ $x=(1/2)^4$
⇒ $x= \frac{1}{16}$

3 0

3 years ago

J. Explain how an atom's valence electron configuration determines its place on the periodic table.

Darya [45]

Answer:

Elements having same valence electrons are placed in same group.

Explanation:

First, let's start with some basic concepts of modern periodic table:

1. Modern Periodic table : It is the arrangement of element in the increasing order of their atomic numbers

The Modern periodic table is divided into Periods and groups .

Periods : These are the horizontal rows. There are seven periods in the periodic table . Period 1 has 2 element. Period two and three has 8 elements , period 4 and 5 have 18 elements and the period 6 and 7 have 32 elements.

Same period have same number of atomic orbital(Shell)

Group : The group is the vertical columns . There are 18 groups in the modern periodic table.Those element which have same group number will also have same number of electron in their outermost shell. The number of electron in the outermost shell determines the valency of the element.

So, elements showing same valency are placed in same group.

All alkali are place in group 1 and have 1 valance electron in the outermost shell

5 0

3 years ago

Can someone help me with these. I don’t understand how to answer them or do the work

ICE Princess25 [194]

How am I supposed to help you if there's not picture of what the problem is

6 0

3 years ago

What is the element with the symbol Ba?

Vika [28.1K]

Answer:

Barium

Explanation:

-Atomic #56

-5th element inn group 2

- soft

- silvery alkaline earth metal

3 0

3 years ago

Read 2 more answers

What are 6 types of energies except Potential and Kinetic energy.

aivan3 [116]

Answer:

The different types of energy include thermal energy, radiant energy, chemical energy, nuclear energy, electrical energy, motion energy, sound energy, elastic energy and gravitational energy.

Explanation:

Hope this helps :D

7 0

3 years ago