Ans is 'b' i.e. Ordinal This is one of the important question and one of the easiest too. (only if you know how to solve if).There are four scales of measurement:NominalOrdinalIntervalRatioNOMINAL;Nominal scale is used where data is divided into qualitative categories or group such as male/female, black/white, urban/suburban/rural.There is no implication of order or ratio.ORDINAL :Ordinal scale is used where the data can be placed in a meaningful order (eg. Students may be ranked 1st, 2nd & 3rd in their class).However there is no information about the size of the interval-no conclusion can be drawn about whether the difference between the first and second student is same as the difference between the second and third.Variables in the form of mild, moderate and severe are analysed by ordinal scale as they can be arranged in a meaningful order but there is no information about the size of the interval between them.INTERVAL:Interval scale data have the same quality as do ordinal data, in that they can be placed in a meaningful order. In addition these data have meaningful intervals between items which are usually measured quantities.for e.g. on the Celsius scale the difference between 100 degree and 90 degree is the same as the difference between 50 degree and 40 degree. However because interval scales do not have absolute 0, ratios of scores are not meaningful; i.e. 100 degree C is not twice as hot as 50 degree C because 0 degree C does not indicate the complete absence of heat.RATIO:A ratio scale has the same properties as an interval scale; but because it has an absolute zero, meaningful ratios do exist.e.g Weight in grams or pounds, time in seconds or days, B.P in millimeters of mercury and pulse rate are all ratio scale data.The only ratio scale of temperature is the Kelvin scale in which zero degrees indicate an absolute absence of heat, just as zero pulse rate indicate an absolute lack of pulse. Therefore, it is correct to say that a pulse rate of 120 is twice as fast as pulse rate of 60.