a) 

4Na + O₂ ---t^o→ 2Na₂O

Na₂O + H₂O → 2NaOH

2NaOH + CO₂ → Na₂CO₃ + H₂O

Na₂CO₃ + Ca(OH)₂ → 2NaOH + CaCO₃

CaCO₃ ---t^o→ CaO + CO₂

CO₂ + NaOH → NaHCO₃ 

NaHCO₃ + H₂SO₄ → Na₂SO₄ + CO₂ + H₂O

Na₂SO₄ + Ba(OH)₂ → 2NaOH + BaSO₄

b) 

S + O₂ ---t^o→ SO₂

2SO₂ + O₂ ---t^o(V₂O₅)→ 2SO₃

SO₃ + H₂O → H₂SO₄

H₂SO₄ + Cu(OH)₂ → CuSO₄ + 2H₂O

CuSO₄ + FeCl₂ → CuCl₂ + FeSO₄

FeSO₄ + 2NaOH → Fe(OH)₂ + Na₂SO₄

Fe(OH)₂ + 2HCl → FeCl₂ + 2H₂O

2FeCl₂ + Cl₂ → 2FeCl₃

2FeCl₃ + 3Ba(OH)₂ → 2Fe(OH)₃ + 3BaCl₂

2Fe(OH)₃ ---t^o→ Fe₂O₃ + 3H₂O

 Fe₂O₃ + 3H₂SO₄ → Fe₂(SO₄)₃ + 3H₂O

2. There used to have many old buildings 10 years ago

3. I wish a new mall didn't build

4. I have had this wardrobe since my wedding day

5. She hasn't been seen for two years

2. There used to be many old buildings 10 years ago.

3. I wish a new mall weren't built here.

4. I have bought this wardrobe since my wedding day.

5. She hasn't been seen (by me) for two years.

Mary if she could speak some foreign languages
Lan if she was going to visit her aunt the day after
what I was doing
how she was feeling then
what I usually did in my free time
why he why he didn't come there to meet her
why I was so lazy and naughty
like playing soccer, don't you?
goes to school late, doesn't he?
can swim very well, can't you?
is going to the party, isn't she?
was published in Germany in 1550, wasn't it?
are sold all over the world, aren't they?
have been built this year, haven't they?
was given a book, wasn't he?
was bought by Mrs Brown yesterday, wasn't she?
is used every day, isn't it?
be beautiful sights in this village when I lived here

A

A

Câu A

Ta có:
\(\dfrac{x}{10}=\dfrac{y}{5}\)
\(\Rightarrow\dfrac{x}{20}=\dfrac{y}{10}\)  \(\left(1\right)\)
\(\dfrac{y}{2}=\dfrac{z}{3}\)
\(\Rightarrow\dfrac{y}{10}=\dfrac{z}{15}\)  \(\left(2\right)\)
Từ \(\left(1\right)\) và \(\left(2\right)\)
\(\Rightarrow\dfrac{x}{20}=\dfrac{y}{10}=\dfrac{z}{15}\)
Lại có:
\(\dfrac{z}{15}=\dfrac{4z}{60}\)
Áp dụng tính chất của dãy tỉ số bằng nhau,ta có:
\(\dfrac{x}{20}=\dfrac{y}{10}=\dfrac{4z}{60}=\dfrac{x+4z}{20+60}=\dfrac{240}{80}=3\)
\(\Rightarrow x=3\cdot20=60\)
     \(y=3\cdot10=30\)
     \(z=3\cdot15=45\)

Em chỉ cần đáp án hay cần giải luôn nhỉ?

câu 6: bài học: hãy là chính mình, biết sống hết mình, làm tốt những trách nhiệm, bổn phận của bản thân sẽ được mọi người tôn trọng, yêu quý