It's a double replacement reaction, so
3 Ca(OH)2 + 2 H3PO4 --> Ca3(PO4)2 + 6 H2O
Ca3(PO4)2
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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Answer:
reduce using fossil fuels
Explanation:
fossil fuels are increasing our carbon footprint and so are green house gasses but we can't have too little greenhouse gasses or too much greenhouse gasses
The correct answer is: [A]: " <span>∆G=∆H-T∆S ".
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