As we move down the group, the metallic bond becomes more stable and the formation of forming covalent bond decreases down the group due to the large size of elements.
Covalent and metallic bonding leads to higher melting points. Due to a decrease in attractive forces from carbon to lead there is a drop in melting point.
Carbon forms large covalent molecules than silicon and hence has a higher melting point than silicon.
Similarly, Ge also forms a large number of covalent bonds and has a smaller size as compared to that of Sn. Hence melting point decreases from Ge to Sn.
The order will be C>Si>Ge>Pb>Sn.
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Answer:- HBr is limiting reactant.
Solution:- The given balanced equation is:

From this equation, There is 2:6 mol or 1:3 mol ratio between Al and HBr. Since we have 8 moles of each, HBr is the limiting reactant as we need 3 moles of HBr for each mol of Al.
The calculations could be shown as:

= 24 mol HBr
From calculations, 24 moles of HBr are required to react completely with 8 moles of Al but only 8 moles of it are available. It clearly indicates, HBr is limiting reactant.
The balanced chemical reaction is :

Number of moles of Na,
.
Now, from balance chemical reaction we can see that 1 mole of oxygen reacts with 4 moles of sodium.
So, number of moles of oxygen are :

So, amount of oxygen required is :

Therefore, 5.08 gram of oxygen will react with 14.6 gram of sodium.
7 becuse it splits in half
C. CaCl2 is the correct answer