Answer: The correct option is A.
Explanation: In a chemical reaction, reactants react to form a number of products.
For the formation of products, the bonds of the individual reactants must be broken and the bonds of the products must be formed.
For example: Formation of water from hydrogen gas and oxygen gas. Reaction follows:

The Bonds of hydrogen and oxygen molecule are broken and new bonds between hydrogen and oxygen atoms are formed to give water molecule.
Heat
gained in a system can be calculated by multiplying the given mass to the
specific heat capacity of the substance and the temperature difference. It is
expressed as follows:<span>
Heat = mC(T2-T1)
When two objects are in contact, it should be that the heat lost is equal to what is gained by the other. From this, we can calculate things. We do as follows:
</span>Heat gained = Heat lost
mC(T2-T1) = - mC(T2-T1)
31.5C (102.4 - 32.5) = 103.5(4.18)(32.5 - 24.5)
C = 1.57 J/C-g
Hope this helps.
Answer:A
Explanation:
The melting points of solids depend in the relative sizes of ions in the ionic lattice. The smaller the relative sizes of the ions, the higher the lattice energy and the stronger the lattice hence higher melting point. Comparing relative ionic sizes, fluoride ion is lesser in size than chloride ion hence NaF has a higher melting point than NaCl.
Answer:
301.7g
Explanation:
So there's 1 out of 3 are Oxygen.
905 / 3 = 301.7