I can think of 2 off the top of my head first is friction and second is gravity
Answer is: mass number of element is 234.
<span>Alpha particle is nucleus of a </span>helium-4<span> atom, which is made of two </span>protons<span> and two </span>neutrons<span>.
</span>²³⁸U → ²³⁴Th + α (alpha particle).
Alpha decay is radioactive decay<span> in which an </span>atomic nucleus<span> emits an </span>alpha particle<span> (helium nucleus) and transforms into an atom with </span>an atomic number that is reduced by two <span>and </span>mass number<span> that is reduced by four</span><span>.</span>
Answer : The final temperature of the copper is, 
Solution :
Formula used :
where,
Q = heat gained = 299 cal
m = mass of copper = 52 g
c = specific heat of copper = 
= final temperature = ?
= initial temperature = 
Now put all the given values in the above formula, we get the final temperature of copper.
Therefore, the final temperature of the copper is,
Convert all the gases from grams to moles using their molar masses first. Remember that nitrogen and oxygen exist as DIATOMIC gases.
O2 - 25 g / 32 g/mol = 0.78 mol O2
N2 - 15 g / 28.02 g/mol = 0.54 mol N2
He - 10 g / 4.0 g/mol = 2.5 mol He
Add all the moles of gases.
0.78 + 0.54 + 2.5 = 3.82 moles
Divide O2 moles by total moles.
0.78/3.82 = 0.20
