Answer : Option D) 
Explanation : When a positron is getting absorbed it means it will be
so, the
will get converted;
So, the whole reaction will be;
+
---->
.
This will convert the whole element of Cu will get changed into Zn. As, it absorbs by the positron, the atomic number gets increased from 29 to 30.
Answer: 1.77 kg of manganese (IV) oxide reacts to produce 1.12kg of manganese metal.
Explanation:
The balanced chemical equation is:
To calculate the moles, we use the equation:
moles of manganese = 
According to stoichiometry :
3 moles of
is produced by = 3 moles of
Thus 20.4 moles of
is produced by =
of
Mass of
(1kg=1000g)
Thus 1.77 kg of manganese (IV) oxide reacts to produce 1.12kg of manganese metal.
Answer :
An egg cooking is an endothermic reaction.
A candle burning and Plaster & water combining and becoming warm are exothermic reaction.
Salt being added to water, with no change in temperature neither endothermic nor exothermic reaction.
Explanation :
- Endothermic reaction : It is a type of reaction in which energy is absorbed in the form of heat from the surroundings.
- Exothermic reaction : It is a type of reaction in which energy is released in the form of heat from the system.
An egg cooking : In this process, the energy is absorbed in the form of heat.
A candle burning and Plaster & water combining and becoming warm : In both the process, the energy is released in the form of heat.
Salt being added to water, with no change in temperature : In this process, neither energy released nor absorbed.
1. A 2. B 5. B this is all I know hope it helps
Answer : (C) Hafnium is the most likely identity of the given substance.
Solution : Given,
Mass of given substance (m) = 46.9 g
Volume of given substance (V) = 3.5 
First, find the Density of given substance.
Formula used :

Now,put all the values in this formula, we get
= 13.4 g/
So, we conclude that the density of given substance (13.4 g/
) is approximately equal to the density of Mercury and Hafnium (13.53 and 13.31 g/
respectively).
According to the question the substance is solid at room temperature but Mercury is liquid at room temperature. So, Mercury is not identical to the given substance.
Another element i.e, Hafnium is the element whose density is approximately equal to the given substance and also solid at room temperature. And we know that the melting point of solid is high.
So, Hafnium is the most likely element which is the identity of the given substance.