The monochloroderivatives will be obtained by substituting chemically non equivalent hydrogen with chlorine atom, one by one
So the possible monochloro derivatives of 2,4-dimethylpentane (figure 1) are shown in figure (2)
The equation presented above is that of uranium reacting with fluorine forming uranium fluoride.
The chemical reaction can be balanced by carefully studying the equation and balancing the number of atoms of each of the element in both sides of the chemical reaction. That is,
<em> U(s) + 3F₂(g) --> UF₆(g)</em>
It would be a,b,c as the answer. hope this helps!