Open system is a system in which mass or energy can be lost to or gained from the environment. In this case, water and power come from external sources best explains why a washing machine would be considered an open system.
Answer: 1. C. polar covalent: electrons shared between silicon and sulfur but attracted more to the sulfur
2. B) 
3. B) Fluorine
Explanation:
1. A polar covalent bond is defined as the bond which is formed when there is a difference of electronegativities between the atoms.
Electronegativity difference = electronegativity of sulphur- electronegativity of silicon = 2.5 -1.8 = 0.7
Thus as electronegativity difference is less than 1.7 , the cond is polar covalent and as electronegativity of sulphur is more , the electrons will be more towards sulphur.
2. A molecular compound is usually composed of two or more nonmetal elements. Example:
Ionic compound is formed by the transfer of electrons from metals to non metals. Example:
,
and 
3. For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals.
Here K is having an oxidation state of +1 and as the compound formed is KZ, the oxidation state of non metallic element Z should be -1. Thus the element Z is flourine which exists as diatomic gas 
Halogens can be characterized as :
1) High Electronegativity
2) Low melting & boiling points
3) Forms Ionic compounds
4) Non-metallic in nature
Hope this helps!
Symbiosis describes close<span> interactions between two or more different species. There are four main types of symbiotic relationships: mutualism, commensalism, parasitism and competition.</span>
Answer:
Never pour water into acid but acid into water
Explanation:
If water is poured into extremely concentrated acid/bases, the rate of volatility and exothermic reaction is too rapid and might cause a chemical eruption, leading to acid burns.
Safety precautions hence dictate the reverse is practiced.
I believe this is a clear answer.