Considering the reaction of hydrogen and oxygen to produce water. If 24.6 g of water is produced and 2.9 g of hydrogen is used, the amount of oxygen needed is 21.87 grams
The best way to solve this question is to write out the reaction between hydrogen and oxygen that resulted in the formation of water.
So, we have:

From the above reaction;
2 moles of hydrogen gas reacted with 1 mole of oxygen to produce 2 moles of water.
If;
- 1 mole of O₂ = 32 grams of O₂
- 2 mole of H₂O = 2 × 18 grams of H₂O
- 2 mole of H₂O = 36 grams of H₂O
We can deduce that since 1 mole of O₂ produced 2 moles of H₂O;
Thus, 32 grams of O₂ is needed to produce 36 grams of H₂O.
∴
To produce, 24.6 grams of H₂O, we have:

= 21.87 grams of oxygen.
Therefore, we can conclude that the amount of oxygen needed is 21.87 grams.
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It has 4 valance electrons.
Answer:
Ba
Explanation:
Magnesium is the element of second group and third period. The electronic configuration of magnesium is - 2, 8, 2 or
There are 2 valence electrons of magnesium.
Fluorine is the element of seventeenth group and second period. The electronic configuration of fluorine is - 2, 7 or
There is 1 valence electron of fluorine.
They will combine and form 
<u>The same type of compound is formed by the other members of the group 2 since they will have 2 valence electron.</u>
Group 2 includes:- beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
Hence, correct options is:- Ba
Answer:
The answer is:
c) Is conducted below the recrystallisation temperature
Explanation:
In cold working the metal goes through a process of plastic deformation that is conducted below its recrystallization point (which its usually at room temperature), this in order to change permanently the makeup of its crystals. The temperature at which the process happens is low enough so that atoms cannot rearrange themselves.
The resulting metal is more resistant to deformation, and has an increased hardness and tensile strength.