Answer : The time passed by the sample is, 
Explanation :
Half-life = 30.0 min
First we have to calculate the rate constant, we use the formula :



Now we have to calculate the time passed.
Expression for rate law for first order kinetics is given by:

where,
k = rate constant = 
t = time passed by the sample = ?
a = initial amount of the reactant = 4.5 mg
a - x = amount left after decay process =0.25 mg
Now put all the given values in above equation, we get


Therefore, the time passed by the sample is, 
Answer:

Explanation:
Hello,
Based on the given chemical reaction, as 31.2 mL of hydrogen are yielded, one computes its moles via the ideal gas equation under the stated conditions as shown below:

Now, since the relationship between hydrogen and magnesium is 1 to 1, one computes its milligrams by following the shown below proportional factor development:

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The answer is C. The payoff of most risks is insignificant.
Electron affinity is a measure of the tendency of a neutral atom to gain electrons and form a negative ion. It can be represented by a general equation:
X + e- → X-
The value of electron affinity decreases on moving down a group. This is because on moving down a group the atomic size increases as a result the added electron feels less pull or attraction towards the nucleus.
In group 14, Carbon 'C' is the first member and therefore will have the highest electron affinity.
Ans : A) Carbon
Answer: B.)
Explanation: Heat flows from pan to sounroundings