Is there meant to be a photo here? there are no options so we can’t answer the question.
There is a shortcut trick while doing such fill in the blanks of nuclear reactions of hydrogen and helium
Let a,b,care elements of set N

Now
for our question
Hence b=4-3+1=1+1=2
So
The missing place should b e deuterium of heavy water
In nuclear reactions energy is released so it's mentioned on product side not reactant side
Dropping a 50 gram piece of metal with a temperature of 125° Celsius into 1000 grams of water at 20° Celsius would lead to a heat loss by the metal and an heat gain by the water. These loss and gain should be equal since energy cannot be created nor destroyed.
This is false, they have intermediate properties between suspension and true solution