The answer is: [B]: "ionic salt" .
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Note: There is no "sharing of electrons" among the elements in this compound; so this compound in NOT a "covalent molecule".
However, there is ionic bonding: Cu²⁺ and Cl⁻ ; to form: "CuCl₂" .
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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 is: density of the substance, energy of the substance, intermolecular bonds between particles.
Melting is a physical change (process), the same substance is present before and after the change, so chemical bonds and melting point of the substance are not changed.
Density of liquids are usually less than in solids, because atoms are further apart.
Liquids have higher energy and atoms or molecules move faster.
Intermolecular bonds are weaker in liquids.
<span>This family of elements is headed by boron. In this case, atomic size increases as one goes down the periodic table, as there are more electrons in each successive element needed to fill the outer shells. As such, thallium, at the lowest level of the group 3a column, will have the largest atomic size.</span>
Answer:
S²⁻(aq) + Cr²⁺(aq) ⇄ CrS(s)
Explanation:
The molecular equation includes all the species in the molecular form. Usually, it is useful to write this first to balance the equation. This is a double displacement reaction.
K₂S(aq) + Cr(NO₃)₂(aq) ⇄ 2 KNO₃(aq) + CrS(s)
The full ionic equation includes all ions and the species that no dot dissociate in water.
2 K⁺(aq) + S²⁻(aq) + Cr²⁺(aq) + 2 NO₃⁻(aq) ⇄ 2 K⁺(aq) + 2 NO₃⁻(aq) + CrS(s)
The net ionic equation includes only those ions that participate in the reaction and the species that do not dissociate in water.
S²⁻(aq) + Cr²⁺(aq) ⇄ CrS(s)
