1 , in -> on

2 , Do -> Does

3 , tower -> towers

4 , city -> cities

5 , is -> are

6 , more busy -> busier 

7 , big -> bigger

8 , do -> does

9 , at -> in

10 , because -> so

Exercise 2 . Underline one mistake in each sentence and correct it.

1. I live on  the twenty-one  floor of City Tower.

=> in

2. Do your brother  live in a small house?

=> Does 

3. There are two high tower  near my house.

=> towers

4. Ha noi is one of the most beautiful city in Viet Nam.

 => cities 

5. These cities is large and busy.

=> are

 6. Living in a big city is  more busy than living in the countryside.

=> busier 

7.  This building is big than that one.

=> bigger

8. What do your hometown ? – it is beautiful.

=> does

9. My best friend, Lisa s living at the mountains.

=> in

10. It is a nice and big  city, because I want to live there.

=>  so

gfvfvfvfvfvfvfv555

\(NTK_X=16.8,5=136đvC\)

Vậy không có nguyên tố X thoả mãn

\(NTK_X=16\cdot8,5=136dvC\)

Vậy không có số nguyên tố X thỏa mãn

gfvfvfvfvfvfvfv555

ghhhhhcfyuhjgyujhf

ghhhhhcfyuhjgyujhf

ai giúp mình k cho

bùi nguyên phương lớp 7 học hóa cô yến đúng ko

Na2(CO3)

\(p+n+e=62\)

\(A=p+n< 43\)

\(\rightarrow p>62-43=19\)

\(p\le n\le1,5p\)

\(\rightarrow3p\le2p+n\le3,5p\)

\(\rightarrow3p\le62\le3,5p\)

\(\rightarrow17,7\le p\le20,67\)

\(\rightarrow19< p\le20,67\)

\(\rightarrow p=20\)

\(\rightarrow\hept{\begin{cases}p=e=20\\n=22\end{cases}}\)

\(\rightarrow m_{\text{nguyên tử}}=m_p+m_e+m_n=20.1,66.10^{-24}+20.9,1.10^{-27}+22.1,66.10^{-24}=6,9902.10^{-23}g\)

\(p+n+e=62\)

\(A=p+n< 43\)

\(\rightarrow p>62-43=19\)

\(p\le n\le1,5p\)

\(\rightarrow3p\le2p+n\le3,5p\)

\(\rightarrow\hept{\begin{cases}p=e=20\\n=22\end{cases}}\Leftrightarrow6,9902\cdot10^{-23}g\)

\(n_{NaOH}=0,24.1,25=0,3mol\)

Nếu muối là \(Na_2CO_3\)

\(\rightarrow n_{Na_2CO_3}=0,5n_{NaOH}=0,15\)

\(\rightarrow m_{Na_2CO_3}=0,15.106=15,9< 25,35\)

Nếu muối là \(NaHCO_3\)

\(\rightarrow n_{NaHCO_3}=n_{NaOH}=0,3\)

\(\rightarrow m_{NaHCO_3}=0,3.84=25,2< 25,35\)

Vậy tạo muối \(\hept{\begin{cases}x\left(mol\right)=Na_2CO_3\\y\left(mol\right)=NaHCO_3\end{cases}}\)

Bảo toàn Na là \(2x+y=0,3\)

Mặt khác \(106x+84y=25,35\)

Ta giải được nghiệm âm

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