The less mass an object has, the greater its gravitational force.
Answer: option A. acidic
Explanation: acidic solution is characterized by the presence of Hydrogen ion.
Answer:
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Explanation:
Half-life is the time taken for the concentration of the substance to reduce by 50%. The original sample of strontium had a mass of 1.6 gms. Thus, option d is correct.
<h3>What is half-life?</h3>
The half-life of any radioactive substance is the time period at which the concentration will get reduced to half the initial amount. The initial mass of Sr-90 is calculated as,

Given,
Quantity of the remaining substance N (t) = 0.40 gm
Initial radioactive substance quantity
=?
Time duration (t) = 56 years
Half-life = 28 years
Substituting values above:

= 1.6 gm
Therefore, option d. the initial mass of Sr is 1.6 gm.
Learn more about half-life here:
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Explanation:
Rate law is defined as the rate of a reaction is directly proportional to the concentration of reactants at constant temperature.
![Rate \propto [\text{concentration of reactant}]^{n}](https://tex.z-dn.net/?f=Rate%20%5Cpropto%20%5B%5Ctext%7Bconcentration%20of%20reactant%7D%5D%5E%7Bn%7D)
= k ![[\text{concentration of reactant}]^{n}](https://tex.z-dn.net/?f=%5B%5Ctext%7Bconcentration%20of%20reactant%7D%5D%5E%7Bn%7D)
where, k = rate constant
n = order of reaction
For the given reaction, 
Hence, its rate will be as follows.
Rate = ![k[H_{2}][NO]](https://tex.z-dn.net/?f=k%5BH_%7B2%7D%5D%5BNO%5D)
Also, it is known that slowest step in a chemical reaction is the rate determining step.
Hence, for the given rate law correct reaction is as follows.
Step 1 :
(slow)
Balancing this equation it becomes
(slow)
Step 2:
(fast)