Em ơi đăng tách bài ra mỗi lượt đăng 1-2 bài thôi nha!

Bài 2 : (1) liên kết ; (2) electron ; (3) liên kết ; (4) : electron ; (5) sắp xếp electron

Bài 4 : 

$\dfrac{M_X}{4} = \dfrac{M_K}{3} \Rightarrow M_X = 52$

Vậy X là crom,KHHH : Cr

Bài 5 : 

$M_X = 3,5M_O = 3,5.16 = 56$ đvC

Tên : Sắt

KHHH : Fe

Bài 9 : 

$M_Z = \dfrac{5,312.10^{-23}}{1,66.10^{-24}} = 32(đvC)$

Vậy Z là lưu huỳnh, KHHH : S

Bài 10  :

a) $PTK = 22M_{H_2} = 22.2 = 44(đvC)$

b) $M_{hợp\ chất} = X + 16.2 = 44 \Rightarrow X = 12$
Vậy X là cacbon, KHHH : C

Bài 11 : 

a) $PTK = 32.5 = 160(đvC)$

b) $M_{hợp\ chất} = 2A + 16.3 = 160 \Rightarrow A = 56$
Vậy A là sắt

c) $\%Fe = \dfrac{56.2}{160}.100\% = 70\%$

Bài 12 : 

a) $M_{hợp\ chất} = R + 1.4 = M_O = 16(đvC) \Rightarrow R = 12$

Vậy R là nguyên tố cacbon, KHHH : C

b) $\%C = \dfrac{12}{16}.100\% = 75\%$

Bài 13 : 

a) $PTK = 32M_{H_2} = 32.2 = 64(đvC)$

b) $M_{hợp\ chất} = X + 16.2 = 64 \Rightarrow X = 32$
Vậy X là lưu huỳnh, KHHH : S

mn giúp em vs ạ em cần gấp cảm ơn ạ 

làm ơn đi ạ , làm ơn đi , anh Dũng , anh KẺ GIẤU TÊN  giúp em vs , hai anh học lp 7 , 8 mà nên chắc giải được ạ 

Hi Hoa !

here i am at the Superb Summer Camp. Mrs. Huong asks us to write-mail in english. Wow! everything here is in english.

there are 25 kids from different school in Ha Noi. They are all nice and friendly. My new friend is Lien, Phong, Phuc and Linh. This evening we're having a campfire. We're singing and Lien is telling a ghost story! i hope is isn't too scary! tomorrow we're doing a treasure hund in the field. Then in the afernoon we're visiting a milk farm to see how they make milk, cheese and butter. I'm not sure what we're doing on the last day! mrs. Huong hasn't told us yet. I'm sure it will be fun!

i miss you already. please write soon.

Love,

Huyen

Dear Linh,

How are you? I was very happy when I got a letter from you. I am really happy that you spent a wonderful summer holiday in Sa Pa.  And now, I would to tell you about my summer holiday. Last summer I visited Cua Lo beach with my parents. We went there by car. We stayed in Binh Minh hotel for a week.

In Cua Lo, we visited a lot of interesting places: Hon Ngu island, Nguyen Su Hoi temple. But the most exciting for me was visiting Hon Ngu island. It  was fantas and roman.. Food in Cua Lo is extremely delicious. I especially felt excited with the courses from seafood such as "cua rang me, chao ngao or mam ruoc"

Cua Lo's people are very friendly and warm. So, my parents and I felt happy very comfortable at home. Well, I told you everything about my holiday. Trang, what places do you want to visit on your next holiday? Why?

I hope to get the answer from you soon.

     Best wishes,

           Mai

1: Ta có: \(\sqrt{3x-5}=2\)

\(\Leftrightarrow3x-5=4\)

hay x=3

2: Ta có: \(\sqrt{25\left(x-1\right)}=20\)

\(\Leftrightarrow x-1=16\)

hay x=17

Em tách ra mỗi lần hỏi đăng 1-3 bài thôi để nhận hỗ trợ sớm nhất nha em!

Bài 1 

a) 2x+6=0

<=> 2x=-6

x=-3

b) 15 -7x=9-3x

<=> -4x=-6

<=>x=\(\dfrac{3}{2}\)

c) 2(x+1)=5x-7

<=>2x+2=5x-7

<=>-3x=-9x

<=>x=3

pt tích

a) x²-2x=0

x(x-2)=0

x=0 hoặc x-2=0   <=> x=2

b) x(x-3)=0

x=0 hoặc x-3=0 <=> x=3

c) (x-3)(2x+5)=0

\(<=>\begin{cases} (x-3=0)\\ (2x+5=0) \end{cases} \)\(\left[\begin{array}{} (x=3)\\ (x=-5/2) \end{array} \right.\)

d) (x-2)(2x-6)=0

\(<=>\begin{cases} (x-2=0)\\ (2x-6=0) \end{cases} \)\(<=>\left[\begin{array}{} (x=2)\\ (x=3) \end{array} \right.\)