Balance of trade is defined as imports subtracted from exports ( = exports - imports). Which of the following blocks of three years has witnessed the largest average negative balance of trade?

For 2007-2009:

2007: $280 - 240 = 40$

2008: $230 - 260 = -30$

2009: $210 - 280 = -70$

Average = $\frac{40 - 30 - 70}{3} = -20$

For 2015-2017:

2015: $200 - 310 = -110$

2016: $220 - 250 = -30$

2017: $200 - 240 = -40$

Average = $\frac{-110 - 30 - 40}{3} = -60$

For 2014-2016:

2014: $200 - 320 = -120$

2015: $200 - 310 = -110$

2016: $220 - 250 = -30$

Average = $\frac{-120 - 110 - 30}{3} = -86.67$

For 2010-2012:

2010: $200 - 310 = -110$

2011: $220 - 290 = -70$

2012: $210 - 320 = -110$

Average = $\frac{-110 - 70 - 110}{3} = -96.67$

After comparing, the period 2010-2012 has the largest negative average balance of trade at $-96.67$ crores, making it the correct answer.