Answer: The mass of electrons is mostly ignored because electrons are extremely small compared to neutrons and protons.
Explanation: A proton is about 1,836 times the size of an electron.
On the periodic table, the atomic number for each element can be found. This number is found by measuring the weight of 6.02 x 10^23 atoms of the element in grams. Electrons aren't ignored when finding exact math, but for the sake of simplification high school teachers will generally have you only count the number of protons and neutrons when calculating the mass of atoms.
Definition of indirect evidence. : evidence that establishes immediately collateral facts from which the main fact may be inferred : circumstantial evidence.
Answer : The specific heat of tin is, 0.213 J/g.K
Explanation :
Formula used :

where,
q = amount of heat lost = -399.4 J
c = specific heat capacity of tin = ?
m = mass of tin = 25.0 g
= final temperature = 
= initial temperature = 
Now put all the given values in the above formula, we get:


Therefore, the specific heat of tin is, 0.213 J/g.K